White level information correction apparatus for image reading apparatus and image reading apparatus with white level information correction apparatus

ABSTRACT

The invention provides a white level information correction apparatus for an image reading apparatus suitably used as an image scanner, which is improved in that analog to digital conversion can be performed effectively for originals of different ground colors with a high degree of accuracy. In the image reading apparatus, image information of a paper sheet being transported along a paper transport path is optically read at a fixed location of the paper transport path using an optical image reading unit and analog data obtained by the optical image reading unit are converted into digital data using white level information of the image information as an index to a conversion reference. The white level information correction apparatus comprises a plurality of storage apparatus for storing a plurality of pieces of white level information to be used as indices to the conversion reference, a data magnification variation apparatus for multiplying white level information from a storage apparatus by a coefficient to vary the magnification of the data, and a data write control apparatus for storing white level information varied in magnification by the data magnification variation apparatus into a storage apparatus to update the stored data.

BACKGROUND OF THE INVENTION

1) Field of the Invention

This invention relates to a white level information correction apparatusfor an image reading apparatus which is suitably applied to an imagescanner and an image reading apparatus with such white level informationcorrection apparatus.

2) Description of the Related Art

In recent years, image reading apparatus or image inputting apparatussuch as image scanners have been and are being developed in order toinput image information to a computer (host computer) or a likeapparatus.

In an image reading apparatus of the type mentioned, an analog imagesignal is converted into a digital signal to be sent out to a hostcomputer. In order to convert an analog image signal into a digitalsignal, an analog to digital (A/D) converter is used in which an analogsignal of a white level is used as a reference value for an upper limitand another analog signal of a black level is used as a reference valuefor a lower limit.

Generally, the level of black is fixed corresponding to a value obtainedwhen the output of, for example, a charge coupled device (CCD) is "0".Accordingly, one of those of analog signals obtained from charge coupleddevices by scanning an image which belong to a range (bits) within whichphotosensitive portions of the charge coupled devices are masked is heldby a capacitor or a like element, that is, sampled and held, to use itas the level of black. In contrast, the level of white must be correctedsince it is influenced significantly by the quantity of light of a lamp(the quantity of light relies upon the position of the lamp, the ambienttemperature, the elapsed time after starting of emission of light and soforth) or the level of the back ground of the original.

In order to correct the white level, concentration designation or thelike is performed to vary the slice levels between the white level andthe black level.

However, the conventional technique has a subject to be solved in thatit is not sufficiently effective when the: color of the ground of theoriginal is dark such as a blue print original and consequently analogto digital (A/D) conversion cannot be performed with a high degree ofaccuracy.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a white levelinformation correction apparatus for an image reading apparatus and animage reading apparatus with a white level information correctionapparatus wherein analog to digital conversion can be performedeffectively for originals of different ground colors.

In order to attain the object described above, according to an aspect ofthe present invention, there is provided a white level informationcorrection apparatus for an image reading apparatus wherein imageinformation of a paper sheet being transported along a paper transportpath is optically read at a fixed location of the paper transport pathusing an optical image reading unit and analog data obtained by theoptical image reading unit are converted into digital data using whitelevel information of the image information as an index to a conversionreference, comprising a plurality of storage means for storing aplurality of pieces of white level information to be used as indices tothe conversion reference, data magnification variation means formultiplying white level information from one of the storage means by acoefficient to vary the magnification of the data, and data writecontrol means for storing white level information varied inmagnification by the data magnification variation means into one of thestorage means to update the stored data.

With the White level information correction apparatus, since itcomprises the plurality of storage means for storing a plurality ofpieces of white level information to be used as indices to theconversion reference, the data magnification variation means formultiplying white level information from one of the storage means by acoefficient to vary the magnification of the data, and the data writecontrol means for storing white level information varied inmagnification by the data magnification variation means into one of thestorage means to update the stored data, even in such a case that, forexample, paper sheets whose ground color is white have been read tillnow and blue print paper sheets of a different ground color are to beread subsequently, the white level information correction apparatuscopes with this sufficiently and can perform analog to digitalconversion of image data with a high degree of accuracy.

The storage means may be constituted from memory circuits independent ofeach other and capable of storing a plurality of pieces of white levelinformation to be used as indices to the conversion reference.

Where the storage means are constituted from memory circuits independentof each other and capable of storing a plurality of pieces of whitelevel information to be used as indices to the conversion reference,control of white level information is facilitated.

Alternatively, the plurality of storage means may be constructed from asingle memory circuit having a plurality of storage areas capable ofstoring a plurality of pieces of white level information to be used asindices to the conversion reference.

Where the storage means are constituted from a single memory circuithaving a plurality of storage areas capable of storing a plurality ofpieces of white level information to be used as indices to theconversion reference, a plurality of independent memory circuits neednot be prepared and easy handling is achieved.

The magnification rate of variation of the data magnification variationmeans may be variable.

Where the magnification rate of variation of the data magnificationvariation means is variable, a high degree of freedom is provided forcorrection of a white level.

The data write control means may include selection means for storingwhite level information varied in magnification by the datamagnification variation means into a selected one of the storage meansto update the stored data.

Where the data write control means includes the selection means forstoring white level information varied in magnification by the datamagnification variation means into a selected one of the storage meansto update the stored data, the stored contents of any one of theplurality of storage means can be updated readily.

The data write control means includes first selection means forselectively outputting white level information varied in magnitude bythe data magnification variation means or white level information fromone of the storage means, a white level algorithm circuit for comparingwhite level information selected by the first selection means and dataobtained from the optical image reading unit with each other andcorrecting the white level information in response to a result of thecomparison, and second selection means for storing an output of thewhite level algorithm circuit into a selected one of the plurality ofstorage means to update the stored data.

Where the data write control means includes the first selection meansfor selectively outputting white level information varied in magnitudeby the data magnification variation means or white level informationfrom one of the storage means, the white level algorithm circuit forcomparing white level information selected by the first selection meansand data obtained from the optical image reading unit with each otherand correcting the white level information in response to a result ofthe comparison, and the second selection means for storing the output ofthe white level algorithm circuit into a selected one of the pluralityof storage means to update the stored data, the white level can becorrected between paper sheets having a same ground color.

The white level information correction apparatus may further compriseswitching control means for determining based on data obtained from theoptical image reading unit whether white level information should bevaried in magnitude by the data magnification variation means andautomatically controlling selective switching of the first selectionmeans.

Where the white level information correction apparatus further comprisesthe switching control means for determining based on data obtained fromthe optical image reading unit whether white level information should bevaried in magnitude by the data magnification variation means andautomatically controlling selective switching of the first selectionmeans, even when a paper sheet to be read changes from the last papersheet, variation of the white level can be automatically performedrapidly.

The white level algorithm circuit may include a digital comparisoncircuit for comparing digital white level information selected by thefirst selection means and digital data obtained by the optical imagereading unit with each other, and a white level information correctioncircuit for correcting the white level information in response to aresult of comparison by the digital comparison circuit.

Where the white level algorithm circuit includes the digital comparisoncircuit for comparing digital white level information selected by thefirst selection means and digital data obtained by the optical imagereading unit with each other and the white level information correctioncircuit for correcting the white level information in response to aresult of comparison by the digital comparison circuit, analog circuitsin the entire circuitry and patterns on a printed circuit board of theimage inputting apparatus can be minimized. Further, since thecorrection of the white level is based on digital processing,oscillations, which often occur with an analog comparator, do not occurin a high frequency band. Accordingly, the advantage that an increase instability of operation and in efficiency and certainty in designing canbe achieved is achieved. Further, in this instance, since the digitalcircuit portion of the white level algorithm circuit can be constructedonly from ordinary logical OR and AND gate circuits, it can be includedreadily into a large scale integrated circuit (LSI).

Alternatively, the white level algorithm circuit may include a controlsignal production circuit for comparing digital white level informationselected by the first selection circuit and digital data obtained by theoptical image reading unit with each other and outputting, in responseto a result of the comparison, a control signal indicating that thedigital data has a predetermined value, a counting circuit for countingthe number of times by which a control signal is outputted successivelyin a direction of a line from the control signal production circuit, anda white level information correction circuit for correcting the whitelevel information in response to a count value of the counting circuit.

Where the white level algorithm circuit includes the control signalproduction circuit for comparing digital white level informationselected by the first selection circuit and digital data obtained by theoptical image reading unit with each other and outputting, in responseto a result of the comparison, a control signal indicating that thedigital data has a predetermined value, the counting circuit forcounting the number of times by which a control signal is outputtedsuccessively in a direction of a line from the control signal productioncircuit, and the white level information correction circuit forcorrecting the white level information in response to a count value ofthe counting circuit, similarly as described above, analog circuits inthe entire circuitry and patterns on a printed circuit board of theimage inputting apparatus can be minimized. Further, since thecorrection of the white level is based on digital processing,oscillations, which often occur with an analog comparator, do not occurin a high frequency band. Accordingly, the advantage that an increase instability of operation and in efficiency and certainty in designing canbe achieved is achieved. Further, in this instance, since the digitalcircuit portion of the white level algorithm circuit can be constructedonly from ordinary logical 015 and AND gate circuits, it can be includedreadily into a large scale integrated circuit (LSI).

According to another aspect of the present invention, there is providedan image reading apparatus, comprising a paper transport path alongwhich a paper sheet from which an image is to be read is transported, anoptical image reading unit for optically reading, at a predeterminedlocation of the paper transport path, image information from a papersheet being transported along the paper transport path, analog todigital conversion means for converting analog data obtained by theoptical image reading unit into digital data using white levelinformation of the image information as an index to a conversionreference, and a white level information correction apparatus forcorrecting white level information to be used as an index to theconversion reference of the analog to digital conversion means, thewhite level information correction apparatus including a plurality ofstorage means for storing a plurality of pieces of white levelinformation to be used as indices to the conversion reference, datamagnification variation means for multiplying white level informationfrom one of the storage means by a coefficient to vary the magnificationof the data, and data write control means for storing white levelinformation varied in magnification by the data magnification variationmeans into one of the storage means to update the stored data.

Further objects, features and advantages of the present invention willbecome apparent from the following detailed description when read inconjunction with the accompanying drawings in which like parts orelements are denoted by like reference characters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an aspect of the presentinvention;

FIG. 2 is a block diagram showing an image data processing system of animage reading apparatus to which the present invention is applied;

FIG. 3 is a block diagram schematically showing the construction of acontrol system of the image reading apparatus to which the presentinvention is applied;

FIG. 4 is a schematic side elevational sectional view of the imagereading apparatus to which the present invention is applied;

FIG. 5 is a perspective view showing an outer profile of the imagereading apparatus of FIG. 4;

FIG. 6 is a schematic side elevational view showing an outer profile ofthe image reading apparatus of FIG. 4;

FIG. 7 is a diagrammatic view schematically showing, in side elevation,an arrangement of principal components of the image reading apparatus ofFIG. 4;

FIG. 8 is an exploded perspective view schematically showing a drivingsystem of the image reading apparatus of FIG.

FIG. 9 is a diagrammatic view schematically showing, in side elevation,the driving system shown in FIG. 8;

FIG. 10 is a diagrammatic view schematically showing, in plan, thedriving system shown in FIG. 8;

FIGS. 11(A) and 11(B) are a schematic plan view and a schematic sideelevational view, respectively, showing a paper transport system of theimage reading apparatus of FIG. 4;

FIG. 12 is a schematic side elevational view showing the construction ofan image reading mechanism of the image reading apparatus of FIG. 4;

FIG. 13 is a diagrammatic view schematically showing the construction ofthe optical image reading mechanism shown in FIG. 12;

FIG. 14 is a block diagram showing the construction of a white levelinformation correction apparatus to which the present invention isapplied together with several associated elements;

FIG. 15 is a block diagram showing a white level algorithm circuit ofthe white level information correction apparatus shown in FIG. 14;

FIG. 16 is a block diagram showing another form of the white levelalgorithm circuit of the white level information correction apparatusshown in FIG. 14;

FIG. 17 is a block diagram showing a further form of the white levelalgorithm circuit of the white level information correction apparatusshown in FIG. 14;

FIG. 18 is a time chart illustrating operation of the while levelinformation correction apparatus shown in FIG. 14;

FIG. 19 is a block diagram showing the construction of another whitelevel information correction apparatus to which the present invention isapplied together with several associated elements;

FIG. 20 is a block diagram showing the construction of a further whitelevel information correction apparatus to which the present invention isapplied together with several associated elements;

FIG. 21 is a block diagram showing the construction of an outputtingsection and an output control circuit of the image data processingsystem shown in FIG. 2;

FIG. 22 is a flow chart illustrating operation of the outputting sectionand the output control section shown in FIG. 21;

FIG. 23 is a block diagram showing the construction of an original enddetection circuit of the image data processing system shown in FIG. 2;

FIG. 24 is a time chart illustrating operation of the original enddetection circuit shown in FIG. 23;

FIG. 25 is a sequence diagram illustrating initialization operation of ahopper system of the image reading apparatus of FIG. 4;

FIG. 26 is a sequence diagram illustrating operation of the hoppersystem in an automatic reading mode;

FIG. 27 is a sequence diagram illustrating operation of the hoppersystem in a manual insertion mode;

FIG. 28 is a sequence diagram illustrating operation of a transportsystem of the image reading apparatus of FIG. 4;

FIG. 29 is a similar view but illustrating operation of the transportsystem at a different stage;

FIG. 30 is a similar view but illustrating operation of the transportsystem at another different stage; and

FIG. 31 is a front elevational view showing an operation panel of theimage reading apparatus shown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

a. Aspect of the Invention

Referring first to FIG. 1, there is shown an image reading apparatus inwhich a white level information correction apparatus is incorporatedaccording to an aspect of the present invention. The image readingapparatus includes a paper transport path 310 along which a paper sheet40 from which an image is to be read is transported, and an opticalimage reading unit 410 which optically reads, at a predeterminedlocation of the paper transport path 310, image information from a papersheet 40 being transported along the paper transport path 310.

The image reading apparatus further includes analog to digitalconversion means (A/D conversion means) 60 for converting analog dataobtained by the optical image reading unit 410 into digital data usingwhite level information of the image information as an index to aconversion reference, and a white level information correction apparatus70 for correcting white level information to be used as an index to theconversion reference of the analog to digital conversion means 60.

It is to be noted that digital to analog conversion means (D/Aconversion means) 62 is provided to convert white level information fromthe white level information correction apparatus 70 by digital to analogconversion and provide a resulted analog signal as an index to theconversion reference to the analog to digital conversion means

The white level information correction apparatus 70 includes a pluralityof storage means 72-1 to 72-N (N is an integral number equal to orgreater than 2) for storing a plurality of pieces of white levelinformation to be used as indices to the conversion reference, datamagnification variation means 74 for multiplying white level informationfrom one 72-i (i =1, 2, . . . , N) of the storage means 72-1 to 72-N bya coefficient to vary the magnification of the data, and data writecontrol means 76 for storing white level information varied inmagnification by the data magnification variation means 74 into one 72-iof the storage means 72-1 to 72-N to update the stored data.

The storage means 72-1 to 72-N may be constituted from memory circuitsindependent of each other and capable of storing a plurality of piecesof white level information to be used as indices to the conversionreference or alternatively from a single memory circuit having aplurality of storage areas capable of storing a plurality of pieces ofwhite level information to be used as indices to the conversionreference.

The magnification rate of variation of the data magnification variationmeans 74 may be variable.

The data write control means 76 may include selection means for storingwhite level information varied in magnification by the datamagnification variation means 74 into a selected one 72-i of the storagemeans 72-1 to 72-N to update the stored data.

The data write control means 76 may include first selection means forselectively outputting white level information varied in magnitude bythe data magnification variation means 74 or white level informationfrom one 72-i of the storage means 72-1 to 72-N, a white level algorithmcircuit for comparing white level information selected by the firstselection means and data obtained from the optical image reading unit410 with each other and correcting the white level information inresponse to a result of the comparison, and second selection means forstoring an output of the white level algorithm circuit into a selectedone 72-i of the plurality of storage means 72-1 to 72-N to update thestored data.

The white level information correction apparatus may further compriseswitching control means for determining based on data obtained from theoptical image reading unit 410 whether white level information should bevaried in magnitude by the data magnification variation means 74 andautomatically controlling selective switching of the first selectionmeans.

The white level algorithm circuit may include a digital comparisoncircuit for comparing digital white level information selected by thefirst selection means and digital data obtained by the optical imagereading unit 410 with each other, and a white level informationcorrection circuit for correcting the white level information inresponse to a result of comparison by the digital comparison circuit.

Alternatively, the white level algorithm circuit may include a controlsignal production circuit for comparing digital white level informationselected by the first selection circuit and digital data obtained by theoptical image reading unit 410 with each other and outputting, inresponse to a result of the comparison, a control signal indicating thatthe digital data has a predetermined value, a counting circuit forcounting the number of times by which a control signal is outputtedsuccessively in a direction of a line from the control signal productioncircuit, and a white level information correction circuit for correctingthe white level information in response to a count value of the countingcircuit.

In the image reading apparatus shown in FIG. 1, image information of apaper sheet 40 being transported along the paper transport path 310 isoptically read by the optical image reading unit 410 at thepredetermined location of the paper transport path 310, and analog datathus obtained by the optical image reading unit 410 are converted intodigital data by the analog to digital conversion means 60 using whitelevel information of the image information as an index to a conversionreference. In this instance, the white level information correctionapparatus 70 corrects the white level information to be used as an indexto the conversion reference of the analog to digital conversion means60.

In particular, in the white level information correction apparatus 70, aplurality of pieces of white level information to be used as indices tothe conversion reference are stored in the plurality of storage means72-1 to 72-N (which may be memory circuits independent of each other ora plurality of storage areas of a single memory circuit). Thus, in sucha case that the ground color a paper sheet 40 varies significantly fromthat of the last paper sheet 40, the data magnification variation means74 multiplies white level information from one 72-i (i =1, 2, . . . , N)of the storage means 72-1 to 72-N by a desired coefficient to vary themagnification of the data, and the data write control means 76 storesthe white level information varied in magnification by the datamagnification variation means 74 into one 72-i of the storage means 72-1to 72-N to update the stored data.

When necessary, the magnification rate of variation of the datamagnification variation means 74 is made variable.

Where the data write control means 76 includes the selection means, whenthe white level information varied in magnification by the datamagnification variation means 74 is to be stored into one 72-i of thestorage means 72-1 to 72-N to update the stored data, the one storagemeans 72-i is selected by the selection means.

Where the data write control means 76 includes the first selectionmeans, the white level algorithm circuit and the second selection means,when the white level information varied in magnification by the datamagnification variation means 74 is to be stored into one 72-i of thestorage means 72-1 to 72-N by the data write control means 76, whitelevel information varied in magnitude by the data magnificationvariation means 74 or white level information from one 72-i of thestorage means 72-1 to 72-N is selectively outputted by the firstselection means, and the white level information selected by the firstselection means is compared with data obtained from the optical imagereading unit 410 and the white level information is corrected inresponse to a result of the comparison by the white level algorithmcircuit. Then, the output of the white level algorithm circuit is storedinto one 72-i of the plurality of storage means 72-1 to 72-N selected bythe second selection means to update the stored data.

Where the white level information correction apparatus further comprisesthe switching control means, the switching control means determines,based on data obtained from the optical image reading unit 410, whetherthe white level information should be varied in magnitude by the datamagnification variation means 74 and automatically controls selectiveswitching of the first selection means.

Where the white level algorithm circuit includes the digital comparisoncircuit and the white level information correction circuit, the digitalcomparison circuit compares digital white level information selected bythe first selection means and digital data obtained by the optical imagereading unit 410 with each other, and the white level informationcorrection circuit corrects the white level information in response to aresult of comparison by the digital comparison circuit.

Where the white level algorithm circuit alternatively includes thecontrol signal production circuit, the counting circuit and the whitelevel information correction circuit described above, the control signalproduction circuit compares digital white level information selected bythe first selection circuit and digital data obtained by the opticalimage reading unit 410 with each other and outputs, in response to aresult of the comparison, a control signal indicating that the digitaldata has a predetermined value, and the counting circuit counts thenumber of times by which a control signal is outputted successively in adirection of a line from the control signal production circuit. Further,the white level information correction circuit corrects the white levelinformation in response to a count value of the counting circuit.

Accordingly, the following effects or advantages can be anticipated withthe white level information correction apparatus and/or the imagereading apparatus according to the present invention.

1. Since the white level information correction apparatus comprises theplurality of storage means 72-1 to 72-N for storing a plurality ofpieces of white level information to be used as indices to theconversion reference, the data magnification variation means 74 formultiplying white level information from one of the storage means 72-1to 72-N by a coefficient to vary the magnification of the data, and thedata write control means 76 for storing white level information variedin magnification by the data magnification variation means 74 into oneof the storage means 72-1 to 72-N to update the stored data, even insuch a case that, for example, paper sheets whose ground color is whitehave been read till now and blue print paper sheets of a differentground color are to be read subsequently, the white level informationcorrection apparatus copes with this sufficiently and can perform analogto digital conversion of image data with a high degree of accuracy.

2. Where the storage means 72-1 to 72-N are constituted from memorycircuits independent of each other and capable of storing a plurality ofpieces of white level information to be used as indices to theconversion reference, control of white level information is facilitated.

3. Where the storage means 72-1 to 72-N are constituted from a singlememory circuit having a plurality of storage areas capable of storing aplurality of pieces of white level information to be used as indices tothe conversion reference, a plurality of independent memory circuitsneed not be prepared and easy handling is achieved.

4. Where the magnification rate of variation of the data magnificationvariation means 74 is variable, a high degree of freedom is provided forcorrection of a white level.

5. Where the data write control means 76 includes the selection meansfor storing white level information varied in magnification by the datamagnification variation means 74 into a selected one 72-i of the storagemeans 72-1 to 72-N to update the stored data, the stored contents of anyone of the plurality of storage means can be updated readily.

6. Where the data write control means 76 includes the first selectionmeans for selectively outputting white level information varied inmagnitude by the data magnification variation means 74 or white levelinformation from one 72-i of the storage means 72-1 to 72-N, the whitelevel algorithm circuit for comparing white level information selectedby the first selection means and data obtained from the optical imagereading unit 410 with each other and correcting the white levelinformation in response to a result of the comparison, and the secondselection means for storing the output of the white level algorithmcircuit into a selected one 72-i of the plurality of storage means 72-1to 72-N to update the stored data, the white level can be correctedbetween paper sheets having a same ground color.

7. Where the white level information correction apparatus furthercomprises the switching control means for determining based on dataobtained from the optical image reading unit 410 whether white levelinformation should be varied in magnitude by the data magnificationvariation means 74 and automatically controlling selective switching ofthe first selection means, even when a paper sheet to be read changesfrom the last paper sheet, variation of the white level can beautomatically performed rapidly.

8. Where the white level algorithm circuit includes the digitalcomparison circuit for comparing digital white level informationselected by the first selection means and digital data obtained by theoptical image reading unit 410 with each other and the white levelinformation correction circuit for correcting the white levelinformation in response to a result of comparison by the digitalcomparison circuit, analog circuits in the entire circuitry and patternson a printed circuit board of the image inputting apparatus can beminimized. Further, since the correction of the white level is based ondigital processing, oscillations, which often occur with an analogcomparator, do not occur in a high frequency band. Accordingly, theadvantage that an increase in stability of operation and in efficiencyand certainty in designing can be achieved is achieved. Further, in thisinstance, since the digital circuit portion of the white level algorithmcircuit can be constructed only from ordinary logical OR and AND gatecircuits, it can be included readily into a large scale integratedcircuit (LSI).

9. Where the white level algorithm circuit includes the control signalproduction circuit for comparing digital white level informationselected by the first selection circuit and digital data obtained by theoptical image reading unit 410 with each other and outputting, inresponse to a result of the comparison, a control signal indicating thatthe digital data has a predetermined value, the counting circuit forcounting the number of times by which a control signal is outputtedsuccessively in a direction of a line from the control signal productioncircuit, and the white level information correction circuit forcorrecting the white level information in response to a count value ofthe counting circuit, similarly as described in paragraph 8 above,analog circuits in the entire circuitry and patterns on a printedcircuit board of the image inputting apparatus can be minimized.Further, since the correction of the white level is based on digitalprocessing, oscillations, which often occur with an analog comparator,do not occur in a high frequency band. Accordingly, the advantage thatan increase in stability of operation and in efficiency and certainty indesigning can be achieved is achieved. Further, in this instance, sincethe digital circuit portion of the white level algorithm circuit can beconstructed only from ordinary logical OR and AND gate circuits, it canbe included readily into a large scale integrated circuit (LSI).

b. Embodiment of the Invention

An image reading apparatus according to a preferred embodiment of thepresent invention will be described in detail below with reference tothe accompanying drawings.

1. General Construction of the Image Reading Apparatus

Referring first to FIGS. 4 to 7, there is shown an image readingapparatus according to a preferred embodiment of the present invention.The general structure of the image reading apparatus shown can bedivided into an apparatus body 10 and an apparatus lid unit 20. Theapparatus lid unit 20 is mounted for pivotal motion around a fulcrum 32to open or close the apparatus body 10. When the image reading apparatusis used, the apparatus lid unit 20 is fixed to such a closing conditionas indicated by solid lines in FIGS. 4 to 6 by a body-lid unit lockingmechanism 30. Various other components of the image reading apparatusare mounted on the apparatus body 10 and the apparatus lid unit 20.

Referring to FIGS. 4 and 7, the image reading apparatus includes, ascomponents thereof, a paper supply mechanism 200 which can successivelysupply paper sheets 40 accommodated therein, a paper transport mechanism300 for transporting a paper sheet 40 supplied from the paper supplymechanism 200, an optical image reading mechanism 400 for opticallyreading information on a paper sheet 40 being transported by the papertransport mechanism 300, and a paper stacking mechanism 500 forreceiving a paper sheet 40 discharged from the paper transport mechanism300 to stack such paper sheets 40.

The paper supply mechanism 200 includes a paper supply hopper 210 whichcan accommodate therein paper sheets 40 to be read, a paper supplyroller 220 located above the paper supply hopper 210 for supplying oneof paper sheets 40 accommodated in the paper supply hopper 210 towardthe paper transport mechanism 300, a paper supply roller drivingmechanism 230 for driving the paper supply roller 220 to rotate, a papersupply hopper driving mechanism 240 for driving the paper supply hopper210 to an inclined position in response to the amount of paper sheets 40accommodated in the paper supply hopper 210, and a paper separationmechanism 800 for preventing two or more paper sheets supplied by thepaper supply roller 220 from being fed to the paper transport mechanism300.

The paper supply hopper 210 includes a hopper table 212 supported forpivotal motion on a rotatable shaft 212A located at a rear end portion(right end portion in FIGS. 4 and 7) of the image reading apparatus. Thehopper table 212 is driven at an end portion (left end portion in FIGS.4 and 7) thereof by a rack-and-pinion mechanism 248 (including a pinion248A and a rack 248B) of the paper supply hopper driving mechanism 240so that it is pivoted upwardly and downwardly and adjusted to apredetermined inclined position. The hopper table 212 includes, as shownin FIG. 5, a pair of tiltable paper edge guide members 214 for guidingthe opposite side edges of the paper sheets 40 accommodated in the papersupply hopper 210.

The paper supply hopper driving mechanism 240 includes, as a drivingsource, a hopper motor 242 constituted from a stepper motor. The drivingforce of the hopper motor 242 is transmitted to the rack-and-opinionmechanism 248 by way of a belt-and-pulley mechanism 244.

Meanwhile, the paper supply roller 220 is supported for rocking motionaround an axis of a separation roller 820 by way of a rockable arm 292such that it can be retracted upwardly from a space above the papersupply hopper 210 by a paper supply roller retraction mechanism 270.Such upward retraction of the paper supply roller 220 can be performedartificially. However, in a normal condition wherein no artificial forceis applied to the paper supply roller 220, the paper supply roller 220remains at a position suitably moved down by the weight of the papersupply roller 220 itself or by means of a spring not shown, at which thepaper supply roller 220 is received by the hopper table 212 below. Then,when the paper supply hopper 210 is pivoted, the paper supply roller 220is moved upwardly by a required amount in response to the position ofthe upper face of the paper sheets 40 accommodated in the hopper table212 which is moved upwardly or downwardly by pivotal motion of the papersupply hopper 210.

Referring now to FIGS. 4, 7, 8 and 9, the paper supply roller drivingmechanism 230 for driving the paper supply roller 220 to rotateincludes, as a driving source, a transport motor 342 constituted from astepper motor. The paper supply roller driving mechanism 230 furtherincludes a first belt-and-pulley mechanism 344 and first to third gearmechanisms 852, 856 and 232 interposed between the transport motor 342and the paper supply roller 220. A pick clutch 238 constituted from anelectromagnetic clutch is provided at an inputting portion of thedriving force to the paper supply roller 220 from the third gearmechanism 232.

The paper supply roller driving mechanism 230 is controlled by papersupply roller driving mechanism control means 250 in response to thepaper supplying position (hopper paper supplying position) of the papersupply hopper 210. More particularly, the paper supply roller drivingmechanism control means 250 controls the pick clutch 238 between on andoff states to control operation of the paper supply roller drivingmechanism 230, that is, the rotation condition of the paper supplyroller 220.

The paper separation mechanism 800 includes a separation roller 820, arotation member 830 disposed in an opposing relationship to theseparation roller 820 with a small gap left therebetween, and aseparation roller driving mechanism 850 for driving the separationroller 820 to rotate.

The rotation member 830 is located below the separation roller 820, thatis, nearer to the apparatus body 10 than the separation roller 820, witha small gap left therebetween. The rotation member 830 includes a pairof pulleys 834 and 836 disposed in a spaced relationship from each otherin the paper transporting direction and an endless belt 838 woundbetween and around the pulleys 834 and 836.

The separation roller driving mechanism 850 is constituted fromcomponents substantially common to those of the paper supply rollerdriving mechanism 230 described hereinabove. In particular, as shown inFIGS. 4, 7, 8 and 9, the separation roller driving mechanism 850includes the transport motor 342 described hereinabove as a drivingsource and further includes the first belt-and-pulley mechanism 344 andthe first and second gear mechanisms 852 and 856 interposed between thetransport motor 342 and the paper supply roller 220. A separation clutch854 constituted from an electromagnetic clutch is interposed in thefirst gear mechanism 852. In short, the paper supply roller drivingmechanism 230 has a construction wherein the third gear mechanism 232 isprovided in addition to the separation roller driving mechanism 850. Itis to be noted that operation of the separation clutch 854 is controlledby separation clutch control means 858.

Meanwhile, the paper transport mechanism 300 includes a paper transportpath 310 for transporting a paper sheet 40 supplied thereto from thepaper supply mechanism 200, a plurality of paper transporting rollers320 to 328 disposed along the paper transport path 310, a roller drivingmechanism 340 for driving the paper transporting rollers 320 to 328, androller driving mechanism control means 350 for controlling the rollerdriving mechanism 340, Idler rollers 330 to 338 are providedcorresponding to the paper transporting rollers 320 to 328,respectively.

The paper transport path 310 includes an inclined transport path 312 fortransporting a paper sheet supplied thereto from the paper supplymechanism 200 in an inclined condition, and a paper reversing transportpath 314 provided contiguously to the inclined transport path 312 forreversing the paper sheet 40 transported by the inclined transport path312.

Due to the construction of the paper transport path 310, the posture ofone of the paper sheets 40 supplied from the paper supply hopper 210 ischanged first from a substantially horizontal posture in the papersupply hopper 210 to a rearwardly inclined posture in the inclinedtransport path 312 and is then reversed by the paper reversing transportpath 314, and then, in this posture, the paper sheet 40 is discharged tothe paper stacking mechanism 500.

Consequently, a paper sheet which is directed upwardly in the papersupply hopper 210 is directed downwardly in the paper stacking mechanism500, and the paper sheets 40 accommodated one on another in the papersupply hopper 210 are successively stacked into the paper stackingmechanism 500 without changing the order of them.

Meanwhile, the paper transporting rollers 320 to 328 and the idlerrollers 330 to 338 are disposed in a condition distributed discretely ata distance smaller than the length of the paper sheets 40 in thetransporting direction as seen from FIGS. 4, 7, 8 and 9.

The roller driving mechanism 340 includes the transport motor 342described above as a driving source and further includes a secondbelt-and-pulley mechanism 348 in addition to the first belt-and-pulleymechanism 344. The first and second belt-and-pulley mechanisms 344 and348 will be described here. The first belt-and-pulley mechanism 344includes a pulley 344A mounted on a rotary shaft of the transport motor342, another pulley 344B mounted on a rotary shaft 320A of the papertransporting roller 320, and a belt 346A wound between and around thepulleys 344A and 344B. The second belt-and-pulley mechanism 348 includespulleys 320B to 328B mounted on the rotary shafts 320A to 328A of thepaper transporting rollers 320 to 328, respectively, and a belt 346Bwound between and around the pulleys 320B to 328B.

Accordingly, when the transport motor 342 operates, the driving force istransmitted from the rotary shaft of the transport motor 342 to thepulley 344B by way of the pulley 344A and the belt 346A so that therotary shaft 320A of the paper transporting roller 320 is driven torotate. Further, from the pulley 320B, the rotary shafts 322A to 328A ofthe other paper transporting rollers 322 to 328 are driven to rotate byway of the belt 346A and the pulleys 322B to 328B so that the papertransporting rollers 320 to 328 are driven to rotate simultaneously.

It is to be noted that reference numeral 360 denotes a tension pulley.

The paper transport mechanism 300 described above is schematically shownin FIGS. 10 and 11. Referring to FIGS. 10 and 11, the components areshown such that the paper supply hopper 210 is positioned on the leftside while a paper stacker 510 is positioned on the right side and apaper sheet 40 is transported from the left to the right side reverselyto those in FIGS. 4 to 9 so as to conform to time charts which will behereinafter described.

Referring now to FIG. 12, the optical image reading mechanism 400includes an optical image reading unit 410 having a reading point 422located intermediately of the inclined transport path 312 for opticallyreading information on a paper sheet 40, and image informationextraction control means 440 for controlling extraction of imageinformation read by the optical image reading unit 410.

Referring l:o FIGS. 4 and 7, the optical image reading unit 410includes, in the arrangement shown, two units of a first optical imagereading unit 412 and a second optical image reading unit 414. Theoptical image reading units 412 and 414 are located intermediately ofthe inclined transport path 312, and the first optical image readingunit 412 optically reads information on the front face 42 of a papersheet 40 while the second optical image reading unit 414 optically readsinformation on the rear face 44 of the paper sheet 40.

Here, each of the optical image reading units 412 and 414 is constitutedas an image reading unit of common specifications. For example, FIG. 12is a schematic side elevational view showing the construction of theimage reading unit of common specifications. Referring to FIG. 12, theoptical image reading unit 410 shown includes a fluorescent lamp unit420 serving as a lighting element for irradiating light upon the readingpoint 422 on the inclined transport path 312, a CCD (charge coupleddevice) circuit board 436 including a CCD array 436A (CCD array 436Adenotes a plurality of CCDs arranged in an array) for optically readinginformation on a paper sheet 40, and a video circuit board 438 forprocessing information from the CCD array 436A. It is to be noted thatreference numeral 434 in FIG. 12 denotes a black box.

A light path 418 from the reading point 422 to the CCD array 436A isconstituted from a plurality of (in the arrangement shown, three, firstto third) mirrors 418A, 418B and 418C for reflecting light. A shadingplate 430 and a lens 432 are located intermediately of the light path418 between the mirror 418C and the CCD array 436A so that an image fromthe mirror 418C may be introduced into the CCD array 436A by way of thelens 432 after it is corrected, particularly at peripheral portionsthereof, by the shading plate 430.

Since the light path 418 is formed by the plurality of mirrors 418A,418B and 418C for reflection of light, the light path 418 can have asufficient length while the reading point 422 and the CCD circuit board436 are located at comparatively near locations to each other.Consequently, even where the lens 432 has a great focal length, thereading point 422 can be disposed at a focus position of the lens 432.

A paper sheet 40 from which information has been read by the opticalimage reading mechanism 400 in this manner is discharged from the papertransport mechanism 300 to the paper stacking mechanism 500. Here, atthe terminal end of the paper transport mechanism 300, a paper dischargeroller mechanism 540 is located so that the paper sheet 40 may bedischarged to the paper stacking mechanism 500 while being driven by thepaper discharge roller mechanism 540.

The paper stacking mechanism 500 includes a stacker table 520 having, atthe bottom thereof, the paper stacker 510 on which paper sheets 40 canbe stacked. A paper trailing end guide mechanism 550 for guiding therear end 48 of a paper sheet 40 to be stacked into the paper stacker510.

Referring back to FIGS. 4, 7 and 11, several sensors 610 to 618, 620A to620D and 622 are provided. Thus, operations of the driving systemsdescribed above, that is, operations of the hopper motor 242 of thepaper supply hopper driving mechanism 240, the pick clutch 238 of thepaper supply roller driving mechanism 230, the separation clutch 854 andthe roller driving mechanism 340 of the separation roller drivingmechanism 850, and the transport motor 342 for the separation rollerdriving mechanism 850 and the paper supply roller driving mechanism 230and extraction operations of the image information extraction controlmeans 440 of the first optical image reading unit 412 and the secondoptical image reading unit 414 are controlled in response to detectionsignals from the sensors 610 to 618 and 620A to 620D.

The sensor (SHE) 610 is a hopper empty sensor for detecting whether ornot the paper supply hopper 210 is empty. The sensor (SPK) 612 is apaper supply sensor for detecting whether or not the posture of thepaper supply hopper 210 is in an optimum condition (that is, a hopperpaper supplying position) for supplying a paper sheet. Here, since thepaper supply roller 220 is put into a paper supplying position (optimumcondition) in response to the paper supplying position of the papersupply hopper 210, the sensor 612 actually detects whether or not thepaper supply hopper 210 and the paper supply roller 220 are in theirindividual paper supplying positions. The hopper empty sensor 610 andthe paper supply sensor 612 may each be constituted from, for example, aphoto-interrupter.

The sensor (SF1) 614 and the sensor (SF2) 616 are transport sensors fordetecting a paper sheet 40 is transported by the paper transportmechanism 300. The sensor (SF3) 618 is a discharge sensor for detectingwhether or not a paper sheet 40 is discharged from the paper transportmechanism 300 to the paper stacking mechanism 500. The transport sensors614 and 616 and the discharge 618 may each be constituted from, forexample, a photo-sensor. Here, the transport sensor 614 is atransmission type photo-sensor which includes a light emitting elementand a light receiving element located on the opposite sides of the papertransport mechanism 300, and each of the transport sensor 616 and thedischarge sensor 618 is a reflection type sensor wherein a lightemitting element and a light receiving element are provided as a unitarymember.

The sensor (SB5) 620A, the sensor (SA4) 620B, the sensor (SB4) 620C andthe sensor (SA3) 620D are sheet width detection sensors. The sensor 620Ais a B5 width detection sensor provided for detection of a paper widthof a paper sheet of the "B5 size"; the sensor 620B is an A4/LT widthdetection sensor provided for detection of a paper width of a papersheet of the "A4 size" or "LT size"; the sensor 620C is a B4 widthdetection sensor provided for detection of a paper width of a papersheet of the "B4 size"; and the sensor 620D is an A4/DL width sensorprovided for detection of a paper width of a paper sheet of the "A3size" or "DL size". The sensors 620A to 620D may each be constitutedfrom, for example, a photo-sensor (in the arrangement shown, areflection type photo-sensor is employed).

Meanwhile, the sensor 622 is a bottom sensor for discriminating whetheror not the hopper table 212 of the paper supply hopper 210 is at itslowermost position (bottom position). The sensor 622 may be, forexample, a photo-interrupter.

For starting and stopping operations, setting of an operation conditionand so forth of the image reading apparatus described above, anoperation panel 920 is provided at the front of the image readingapparatus as shown, for example, in FIG. 5.

2. Image Reading Mechanism

The optical image reading unit 410 includes, in the arrangement shown,two units of the first optical image reading unit 412 and the secondoptical image reading unit 414 as described hereinabove. The opticalimage reading units 412 and 414 are located intermediately of theinclined transport path 312, and the first optical image reading unit412 optically reads information on the front face 42 of a paper sheet 40while the second optical image reading unit 414 optically readsinformation on the rear face 44 of the paper sheet 40.

As described above, since the optical image reading units 412 and 414are constructed as image reading units of common specifications, whenthere is no necessity of distinguishing them from each other in thedescription of each optical image reading unit, the optical imagereading unit is represented by the optical image reading unit 10. Inparticular, the light path 418 from the reading point 422 to the CCDcircuit board 436 in the optical image reading unit 410 is schematicallyshown in FIG. 13 wherein the light path 418 is generally represented asa straight line omitting the reflections by the mirrors 418A, 418B and418C. Referring to FIG. 13, pieces of image information arranged in thewidthwise direction of a paper sheet 40 are collected by the lens 432and come to the CCD circuit board 436. The CCD circuit board 436 isconstituted from a plurality of CCDs arranged in a juxtaposedrelationship to each other so as to catch the pieces of informationarranged in the widthwise direction.

The shading plate 430 located forwardly of the lens 432 corrects theimage information since the image information is distorted by anincreasing amount toward the opposite left and right ends and of thepaper sheet 40.

The CCD array 436A operates under the control of respective CCD driversto catch image information, and the image information is sent to andprocessed by a video circuit provided on the video circuit board 438.

By the way, in each of the optical image reading units 410, thefluorescent lamp unit 420 is provided in order to make the reading point422 light.

It is to be noted that a heater (not shown) is provided along the rearface of the fluorescent lamp of the fluorescent lamp unit 420. When thetemperature is low, the heater is rendered operative, and after it isstarted, the fluorescent lamp is warmed up rapidly so that the readingpoint 422 can be illuminated with a sufficient amount of light.

3. Read Image Data Processing

3-1. Outline of the Read Image Data Processing System

Referring to FIG. 2, the image reading apparatus includes a first imagedata processing system D1 for processing image data read by the firstoptical image reading unit 412 for reading information on the front faceof a paper sheet, and a second image data processing system D2 forprocessing image data read by the second optical image reading unit 414for reading information on the rear face of the paper sheet.

The first image data processing system D1 includes a CCD array 436AA ofthe first optical image reading unit 412, an amplification circuit (AMP)64A, a sample hold circuit 66A, an analog to digital (A/D conversioncircuit 60A, and an image processing section 68A. Meanwhile, the secondimage data processing system D2 includes a CCD array 436AB of the secondoptical image reading unit 414, an amplification circuit 64B, a samplehold circuit 66B, an analog to digital conversion circuit 60B and animage processing section 68B.

The CCD arrays 436AA and 436AB read image data of a paper sheet by wayof the image reading units 412 and 414, respectively, as describedhereinabove. The amplification circuits 64A and 64B amplify the imagedata of the paper sheet obtained from the CCD arrays 436AA and 436AB,respectively, and the sample hold circuits 66A and 66B sample and holdthe image data of the paper sheet after amplified by the amplificationcircuits 64A and 64B, respectively.

The analog to digital conversion circuits 60A and 60B convert analogdata obtained from the image reading units 412 and 414 into digital datausing white level information and black level information of the imageinformation of the paper sheet as indices for a conversion criterion.The image processing sections 68A and 68B process the digital data fromthe analog to digital conversion circuits 60A and 60B, respectively, byvarious processes such as binary digitization, emphasis and smoothing.

The image data processing system further includes an outputting section90 for selectively sending out paper front face image data and paperrear face image data to a host computer (not shown) in response to aninstruction from an output control circuit 100 which is part of theimage information extraction control means 440. In particular, in thepresent embodiment, since the image reading units 412 and 414 areprovided in the proximity of each other, it sometimes occurs that theimage reading units 412 and 414 read images simultaneously. Therefore,information from the second optical image reading unit 414 for readinginformation on the rear face of a paper sheet is stored once into abuffer storage apparatus (DRAW) of the rear face reading board 944(refer to FIG. 3) and, after information from the first optical imagereading unit 412 is sent to the host computer, the information from thesecond optical image reading unit 414 is sent from the buffer storageapparatus to the host computer. Such control means is provided in theoutputting section 90, and details of the same will be hereinafterdescribed.

In this manner, image information read by the image reading units 412and 414 is read out under the control of the output control circuit 100of the image information extraction control means 440 as seen from FIG.7. In this instance, in the image information extraction control means440, transfer control of image information to the host computer and likecontrol are performed in response to results of detection of a paperleading end detection circuit (paper leading end detection means) 450and a paper trailing end detection circuit (paper trailing end detectionmeans) 451. It is to be noted that the paper leading end detectioncircuit 450 and the paper trailing end detection circuit 4S1 will behereinafter described.

In particular, the paper leading end detection circuit 450 detects thepaver leading end 46 from a variation of the output of each of theoptical image reading units 410, and the rarer trailing end detectioncircuit 451 detects the paper trailing end 48 from a variation of theoutput of each of the optical image reading units 410. The paper leadend detection circuit 450 and the paper trailing end detection circuit4S1 are both provided in the image information extraction control means.It is to be noted that also the raper leading end detection circuit 450and the paper trailing end detection circuit 451 will be hereinafterdescribed.

Further, the image information extraction control means 440 controlsextraction of image information obtained from the first optical imagereading unit 412 and the second optical image reading unit 414 inresponse to a result of selection by the original selection switch 924Lserving as the paper reading selection means and a discrimination mark(not shown) applied to a paper sheet 40.

In particular, it can be selected by the original selection switch 924Lwhether both face reading should be performed or one face reading shouldbe performed, and the image information extraction control means 440performs reading control in response to a result of the selection by theoriginal selection switch 924L. However, paver sheets which require bothface reading and paver sheets which allow one face reading may possiblybe present in a mixed condition. In this instance, when paper sheetsshould be read in a different manner from other paper sheets in whichthe paper sheets are mixed, a discrimination mark is applied to each ofthe paper sheets so that they may be read in a different manner. Thediscrimination mark is provided for discrimination whether the papersheet should be read by one face reading or by both face reading, and isapplied to a location outside an original reading area such as, forexample, a corner of the leading end of the paper sheet 40 so that itmay be distinguished from image information in the original reading areawhich should originally be read.

Therefore, for example, when one face reading originals are mixed inboth face reading originals, if a discrimination mark which designatesone face reading is applied to each of the one face reading originalsthe quantity of which is smaller than that of the both face readingoriginals and it is selectively set by way of the original selectionswitch 924L that both faces of each paper sheet 40 should usually beread, then image information on both faces of a paper sheet is normallyread by both of the first optical image reading unit 412 and the secondoptical image reading unit 414. However, when a discrimination mark 50is detected, image information only on the front face or the rear faceof the paper sheet 40 is read by the first optical image reading unit412 or the second optical image reading unit 414.

On the contrary, when both face reading originals are mixed in one facereading originals, if a discrimination mark which designates double facereading is applied to each of the double face reading originals thequantity of which is smaller than that of the one face reading originalsand it is selectively set by way of the original selection switch 924Lthat one face of each paper sheet 40 should usually be read, then imageinformation only on the front face or the rear face of a paper sheet isnormally read by the first optical image reading unit 412 or the secondoptical image reading unit 414. However, when a discrimination mark isdetected, image information on the both faces of the paper sheet is readby both of the first optical image reading unit 412 and the secondoptical image reading unit 414.

The image information extraction control means 440 further includesdiscrimination mark image erasure means 460 so that the image of suchdiscrimination mark applied to a paper sheet 40 may be erased and onlyimage information to be read originally may be outputted.

By the way, the apparatus body 10 or the apparatus lid 20 assures anupper mounting space (space for the front face reading unit) 26 and alower mounting space (space for the rear face reading unit) 16 havingsubstantially similar sizes and shapes to each other to allow theoptical image reading units 412 and 414 to be mounted in them,respectively (refer to FIG. 4). In the meantime, the optical imagereading unit 410 is prepared by a plural number having differentspecifications having different performances but having substantiallycommon sizes and profiles.

While, in the image reading apparatus of the present embodiment, thefirst optical image reading unit 412 and the second optical imagereading unit 414 are constructed with common specifications, it is easyto construct the first optical image reading unit 412 and the secondoptical image reading unit 414 so as to have different specificationssuch that, for example, the optical image reading unit for front facereading of the construction described above has higher performances thanthe optical image reading unit for rear face reading of the constructiondescribed above.

Further, each of the optical image reading units 410 includes detectionmeans (front/rear face detection means) 630 which can detect that it isinstalled as a unit for front face reading when it is installed in theupper mounting space 26 but detect that it is installed as a unit forrear face reading when it is installed in the lower mounting space 16.The detection means 630 may be constructed such that, for example, afront surface detection projection (not shown) is provided only in theupper mounting space 26 while a rear face detection projection (notshown) is provided only in the lower mounting space 16, and a front facedetection switch (not shown) which is automatically contacted, when itis installed in the upper mounting space 26, by the front face detectionprojection to switch to an on-state and a rear face detection switch(not shown) which is automatically contracted, when it is installed inthe lower mounting space 16, by the rear face detection projection toswitch to an on-state are provided on each of the optical image readingunits 410.

Information detected by the detection means 630 in this manner is sentto the image information extraction control means 440 and used forextraction control of image information.

The image data processing system shown in FIG. 2 further includes a pairof timing circuits 55A and 55B which define, for example, sample holdingtimings of the sample hold circuits 66A and 66B, respectively.

3-2. White Level Information Used upon Analog to Digital Conversion ofImage Data and Associated Factors

As shown in FIG. 2, each of the analog to digital conversion circuits60A and 60B includes a white level information correction circuit (whitelevel information correction apparatus) 70A or 70B and a black levelsetting circuit 61A or 61B.

The white level information correction circuits 70A and 70B individuallyset white level information to be used as indices for a conversioncriterion of the analog to digital conversion circuits 60A and 60B,respectively, and suitably correct the thus set while level information.The black level setting circuits 61A and 61B individually set blacklevel information to be used as indices for a conversion criterion ofthe analog to digital conversion circuits 60A and 60B, respectively. Itis to be noted that the black level setting circuits 61A and 61B areeach constructed as a sample hold circuit.

The white level information correction circuits 70A and 70B will bedescribed in more detail below. Here, since the white level informationcorrection circuits 70A and 70B have a same construction, referencecharacters to components of the white level information correctioncircuits 70A and 70B are not distinguished between A and B.

In particular, referring to FIG. 14, the white level informationcorrection circuit 70 includes a plurality of (for example, two) memorycircuits 72-1 and 72-2 and registers 73-1 and 73-2, selection circuits75a, 75b, 75c and 75d, a data magnification variation circuit 74, awhite level algorithm circuit 77, and so forth.

The memory circuits 72-1 and 72-2 store a plurality of pieces of whitelevel information (individual pieces of white level informationcorrespond to originals having different ground colors) to be used asindices for a conversion criterion. Write/read control of each of thememory circuits 72-1 and 72-2 is performed in response to an instructionwhich is received from an MPU (microprocessor unit) circuit 150 by anaddress controller 72b by way of an input/output port (I/O port) 72a. Itis to be noted that a RAM (random access memory) may be employed for thememory circuits 72-1 and 72-2.

The registers 73-1 and 73-2 serve as buffer circuits for temporarilystoring the outputs of the memory circuits 72-1 and 72-2, respectively.Each of the selection circuits 75a, 75b, 75c and 75d, selectivelyoutputs desired data to a required output line. For example, amultiplexer is used for the selection circuits 75a, 75b, 75c and 75d.

In particular, the selection circuit 75a selectively outputs data fromthe register 73-1 or 73-2 to the data magnification variation circuit 74side. The selection circuit 75b selectively outputs white levelinformation varied by magnification variation by the data magnificationvariation circuit 74 or white level information from the memory circuit72-1 or 72-2. The selection circuit 75c stores the output of the whitelevel algorithm circuit 77 into and updates a required one of the memorycircuits 72-1 and 72-2. The selection circuit 75d supplies the output ofone of the memory circuits 72-1 and 72-2 to the analog to digitalconversion circuit 60 side by way of a digital to analog conversioncircuit 62 (actually, analog to digital conversion circuits 62A and 62Bare provided in the data processing systems D1 and D2, respectively).

The data magnification variation circuit 74 varies data by magnificationvariation by multiplying white level information from the memory circuit72-1 or 72-2 by a desired coefficient (m: in order to lower the whitelevel, a value between 1 and 0 is selected for m, but in order to raisethe white level, a value higher than 1 is selected for m). For example,a digital multiplier is used for the data magnification variationcircuit 74. Further, the magnification variation coefficient m of thedata magnification variation circuit 74 can be varied by an instructionfrom the MPU circuit 150.

The white level algorithm circuit 77 compares white level informationand data obtained from the optical image reading unit 410 with eachother and corrects the white level information in accordance with aresult of the comparison. Referring to FIG. 1S, the white levelalgorithm circuit 77 includes a video signal comparator 77a serving as adigital comparison circuit for comparing digital white level informationselected by the selection circuit 75b and digital data obtained from theoptical image reading unit 410 with each other, and an addition circuit77b serving as a white level information correction circuit forcorrecting the white level information in accordance with a result ofthe comparison by the video signal comparator 77a.

The white level information correction circuit 70 will be described inmore detail.

Referring first to FIG. 14, analog video signals from the CCD arrays436AA and 436AB are amplified by the amplification circuits 64A and 64B,respectively, and, for example, those analog video signals of theoutputs of the amplification circuits 64A and 54B in portions (bits) inwhich photosensitive portions of the CCD arrays 436AA and 436AB aremasked are sampled and held by black level setting circuits (sample holdcircuits) 71A and 71B, respectively. The thus held analog video signalsare connected as reference signals for a black level to the lower limitsides (VRB) of the analog to digital conversion circuits 60A and 60B.Meanwhile, reference signals for a white level are obtained byconverting white level values in lines obtained in the last scanningcycle and stored in the memory circuit 72-1 or 72-2 into analog signalsby means of the digital to analog conversion circuits 62A and 62B, andare connected to the upper limit sides (VRT) of the analog to digitalconversion circuits 60A and 60B, respectively.

Consequently, the analog to digital conversion circuits 60A and 50Boutput digital signals on the scale of 256 gradations between the whitereference level (VRT) and the black reference level (VRB). In thisinstance, for the white reference level, an analog value of a whitelevel produced corresponding to a white level obtained in the lastscanning cycle for an image is used, and for the black reference level,an analog value of a dot at which the photosensitive portion of the CCDarray 436AA or 436AB is masked is used.

By the way, white reference level data extracted from the memory circuit72-1 or 72-2 is fetched into the corresponding register 73-1 or 73-2,and one of the outputs of the registers 73-1 and 73-2 is selected by theselection circuit 75a and then multiplied by m by the data magnificationvariation circuit 74.

Further, the output of the data magnification variation circuit 74 ordata extracted from the memory circuit 72-1 or 72-2 is selected by theselection circuit 75b and inputted to the terminal b of the white levelalgorithm circuit 77.

Meanwhile, a digital value of a video signal which is the output of theanalog to digital conversion circuit 60 is inputted to the otherterminal a of the white level algorithm circuit 77. Consequently, thethus inputted digital value is inputted to comparators (COMP) 77a-0 to77a-2 of the video signal comparator 77a shown in FIG. 15 and thenoutputted from the video signal comparator 77a as one of, for example,three different outputs including X"FF" (white represented by X"FF" bythe 256 gradation representation), X"F7" to X"FE" (a little dark whiterepresented by X"F7" to X"FE" by the 256 gradation representation) andX"F6" or less (white represented by X"F6" or less by the 256 gradationrepresentation).

In the video signal comparator 77a, when the comparators (COMP) 77a-0 to77a-2 detect that the digital output of the analog to digital conversioncircuit 60 is X"FF" mentioned above (that is, when a coincidence outputis obtained), it is recognized that the analog video signal obtained byscanning of the current scanning line of the image is equal to or muchhigher than a white level obtained by scanning in the last scanningcycle, and the white level value of the preceding cycle is incremented,for example, by one.

However, when it is detected that the digital output of the analog todigital conversion circuit 60 falls within the range from X"FE" toX"F7", it is recognized that the analog video signal is a little lowerthan the white level obtained in the last scanning cycle, and the whitelevel value of the last cycle is incremented by, for example, "-1", thatis, decremented by one. Particularly, since no carry need be taken intoconsideration, X"FF", which is a complementary number on 2, should beadded.

When it is detected that the digital output of the analog to digitalconversion circuit 60 is equal to or lower than X"F6", it is recognizedthat not the white level varies but the image now is on the gray leveland is considered that it is not related to correction of the whitelevel, and such control as to perform nothing (particular, to add X"00")is performed to calculate a new white level and determine the new whitelevel as a correction value for scanning of the present scanning line.

When one of the comparators (COMP) 77a-0, 77a-1 and 77a-2 outputs "1",only a corresponding one of gate circuits (DV) 77a-3 to 77a-5 in thevideo signal comparator 77a outputs the value to be added (X"01", X"FF"or X"00" in FIG. 15) while the other gate circuits (DV) exhibit a highimpedance state. For example, when the output is extracted from the gatecircuit 77a-3, the other gate circuits 77a-4 and 77a-5 exhibit a highimpedance state. Thus, the gate circuits 77a-3 to 77a-5 operate astri-state elements.

Then, the output from one of the gate circuits (DV) 77a-3 to 77a-5outputted from the video signal comparator 77a is added to a digitalvalue (W0 to W7 in the last cycle) of the white level of the last cycle,which is the output of the selection circuit 75b, by the additioncircuit 77b. Then, a result of the addition is outputted as a correctionvalue (W0 to W7 in the present cycle) of the white level for the presentscanning cycle from the terminal c of the white level algorithm circuit77 and is stored into the memory circuit 72-1 or 72-2 selected by theselection circuit 75c . It is to be noted that, as shown in FIG. 15, theaddition circuit 77b is constituted from an adder 77b-0 and a flip-flop77b-1 of one stage. The flip-flop (FF) 77b-1 operates as a hazardprevention mechanism when the correction value in the present cycle isadded to the white level corrected in the last scanning cycle and aresult of the addition is stored into the memory circuit 72-1 or 72-2.

Such new white level values based on analog video signals of pictureelements of a line obtained by scanning the image by means of the CCDarray 436A in such a manner as described above are stored into an areaof one of the memory circuits for corresponding picture elements of theline selected by the selection circuit 75d. Then, each time a next lineis read and analog to digital conversion is performed, the white levelvalues are read out as correction values and are each used as the upperlimit value (VRT) for the analog to digital conversion circuit 60 andfurther referred to for correction of the white level of each pictureelement of the line.

Naturally, processing of scanning a certain line of the image by meansof the CCD array 436A and reading out analog video signals of theindividual picture elements and processing of reading out values ofwhite levels of a line scanned in the last scanning cycle from thememory circuit 72-1 or 72-1 are synchronized with a shift pulse signalused to scan the image by means of the CCD array 436A, and the addressin the scanning line and the address of the memory circuit 72-1 or 72-2described hereinabove (the address of the memory circuit of the 8 Kwordcapacity) are synchronized with each other with an offset of oneaddress.

Further, in the white level information correction circuit 70, forexample, in such a case that paper sheets whose ground color is whitehave been read till now and blue print paper sheets of a differentground color are to be read subsequently, the white level value to beprovided to the analog to digital conversion circuit 60A or 60B isvaried in response to an instruction signal from the MPU circuit 150when a manual instruction or an automatic instruction is provided to theMPU circuit 150. To this end, white level information stored in thememory circuit 72-1 (or 72-2) is taken out and stored into the register73-1 (or 73-2), and then the output of the register 73-1 is selected bythe selection circuit 75a so that it is subsequently multiplied by m bythe data magnification variation circuit 74. The magnification variationfactor m can be modified freely in response to an instruction from theMPU circuit 150. This increases the degree of freedom in correction of awhite level.

Then, the output of the data magnification variation circuit 74 isselected by the selection circuit 75b and then processed by requiredprocessing by the white level algorithm circuit 77, and then the whitelevel of the thus varied magnification is stored into the other memorycircuit 72-2 (or 72-1) by way of the selection circuit 75c. Then, thewhite level of the varied magnification is used as a conversionreference of the analog to digital conversion circuit 60.

It is to be noted that signals at several locations of the circuitryshown in FIG. 14 in this instance (locations denoted at (1) to (8) inFIG. 14, and the output enable signal OE and the write enable signal WEfor a memory circuit) are illustrated in the time chart of FIG. 18.

Thereafter, so far as such blue print paper sheets are used, white levelinformation from the memory circuit 72-2 (or 72-1) in which data of thewhite level information multiplied by m is stored is extracted, and now,the output of the memory circuit 72-2 (or 72-1) is inputted by way ofthe selection circuit 75b to the white level algorithm circuit 77, bywhich the processing described above is performed subsequently so thatthe white level value may have an appropriate value to update the whitelevel.

Consequently, even in such a case that paper sheets whose ground coloris white have been read till now and blue print paper sheets of adifferent ground color are to be read subsequently, the white levelinformation correction apparatus copes with this sufficiently and canperform analog to digital conversion with a high degree of accuracy.Besides, by constructing the correction circuit for a white level from adigital circuit, analog parts in the entire circuit and patterns of aprinted circuit board of an image inputting device can be reduced to theminimum. Further, since correction of a white level is performed bydigital processing, no oscillation occurs in a high frequency bandwhereas it occurs often with an analog comparator. Accordingly, also theadvantage that an increase in stability of operation and in efficiencyand certainty in designing can be achieved is obtained.

Further, the white level algorithm circuit 77 may include, as shown inFIG. 16, a video signal comparator 77c serving as a control signalgeneration circuit for comparing digital white level informationselected by the selection circuit 75b and digital data obtained from theoptical image reading unit 410 with each other and outputting, inaccordance with a result of the comparison, a control signalrepresenting that the digital data is a predetermined value, a countingsection (counting circuit) 77d for counting the number of times by whicha control signal is successively outputted in the direction of a linefrom the video signal comparator 77c, an addition value selectingmultiplexer 77e serving as a white level information correction circuitfor correcting white level information in accordance with a countedvalue of the counting section 77d, and an addition circuit 77f.

In particular, also in this instance, a digital signal from the analogto digital conversion circuit 60 is inputted to comparators (COMP) 77c-0to 77c-2 in the video signal comparator 77c, by which it is divided, forexample, into three different outputs (X"FF", X"F7" to X"FE", and X"F6"or less) by similar operation to that described hereinabove withreference to FIG. 15.

The outputs of the comparators (COMP) 77c-0 to 77c-2 in the video signalcomparator 77c in this instance are outputted by way of gate circuits(G) 77c-3 to 77c-5 and inputted to the counting section (Count) 77d asseen from FIG. 16.

In this instance, each of the memory circuits 72-1 and 72-2 storesinformation of 8 bits (W0 to W7) necessary to store digital values ofwhite levels of ordinary picture elements obtained by scanning in thelast scanning cycle. The 8 bits mentioned above are a new white levelsignal to be used for a next line which has been produced from a digitalvalue outputted from the analog to digital conversion circuit 60described hereinabove and an upper limit signal used thereupon by theanalog to digital conversion circuit 60. Each of the memory circuits72-1 and 72-2 further stores, for example, the output of four bits (Qato Qd) of the counting section (Count) 77d corresponding to each bit ofthe line.

The output signal of the comparator (COMP) (=FF?) 77c-0 mentioned aboveis connected to a count enable (EN) terminal of the counting section(Count) 7d, and the four bits (Qa to Qd) of the count value for eachpicture element obtained by scanning in the last scanning cycle andstored in the memory circuit 72-1 or 72-2 are inputted to terminals Dato Dd of the counting section (Count) 77d. While the count value (Da toDd) is inputted, when the output of the analog to digital conversioncircuit 60A or 60B in the present scanning cycle is X"FF" andconsequently a coincidence signal is outputted from the comparator(COUP) (=FF? ) 77c-0 so that the count enable (EN) terminal of thecounting section (Count) 77d is energized, the counting section (Count)77d counts up the input value (Da to Dd). However, when the count enable(EN) terminal is not energized and the output signal of one of the othercomparators (COUP) (=F7 to FE?, -F6?) 77c-1 and 77c-2, the resetterminal (RST0 or RST1) of the counting section (Count) 77d is energizedso that the count value (Da to Dd) for each picture element is cleared.

In particular, in the counting section (Count) 77d, the count value (Qato Qd) in the last scanning line for each dot of the CCD array 436A isread out from a corresponding address of the memory circuit 72-1 or 72-2in synchronism with a shift pulse for shifting the CCD array 436A and isloaded to the Da to Dd terminals of the counting section (Count) 77c sothat X"FF" which represents a white level is counted for each dot todetermine by what number of success lines X"FF" appears. When thedigitally converted value of the dot falls within the range of X"F7" toX"FE" or X"F6" or less, the count value for the dot loaded to the Da toDd terminals of the counting section (Count) 77d is cleared.

In the addition value selecting multiplexer (correction value conversioncircuit) 77e shown in FIG. 16, one of gate circuits (DV) 77e-0 to 77e-4is selected in response to a signal obtained from a decoder (DEC) 77g bydecoding an output value of the counting section (Count) 77d and signalsα, β and γ(7) outputted from the comparators (COMP) 77c-0, 77c-1 and77c-2 of the video signal comparator 77c by way of the gate circuits (G)77c-3, 77c-4 and 77c-5, respectively, to select an addition value(X"01", "X02" or X"04") to be added to a white level of each pictureelement of a line obtained by the line scanning in the last scanningcycle and stored in the memory circuit 72-1 or 72-2.

The decoded signal from the decoder 77g is "01" when the count value ofthe counting section 77d is "1", that is, when the count value signifiesthat the white level corrected in the last scanning cycle is not X"FF"but the white level in the present scanning cycle is X"FF"; the decodedsignal is "02" when the count value is "02", that is, when the countvalue signifies that the white level corrected in the last scanningcycle is X"FF" and also the white level in the present scanning cycle isX"FF"; and the decoded signal is "03" when the count value is "03", thatis, when the count value signifies that the white level corrected in thesecond last scanning cycle is X"FF" and also the white level correctedin the last scanning cycle is X"FF" and besides also the white level inthe present scanning cycle is X"FF".

Accordingly, when the count value (Qa to Qd) of the counting section(Count) 77d is, for example, "01", it is recognized that the correctedwhite level value in the last scanning cycle was not X"FF", and the gatecircuit (DV) 77e-2 of the addition value selecting multiplexer 77e isselected. Consequently, the input a to the gate circuit (G) 77e-2 isenergized to determine "+1" as the correction value for the white levelvalue of the last scanning cycle so that the correction value "+1" maybe added by the addition circuit 77f.

Similarly, when the count value (Qa to Qd) of the counting section(Count) 77d is, for example, "02", it is recognized that the correctedwhite level value in the last scanning cycle was X"FF" and then thewhite level of the dot in the present scanning cycle is X"FF", and thegate circuit (DV) 77e-3 is selected. Consequently, the input a to thegate circuit (G) 77e-3 is energized to determine "+2" as the correctionvalue for the white level value of the last scanning cycle.

Further, similarly, when the count value (Qa to Qd) of the countingsection (Count) 77d is, for example, equal to or higher than "03", it isrecognized that the successive corrected white level values in the lastscanning cycle and the second last scanning cycle were X"FF" and thenalso the white level of the dot in the present scanning cycle is X"FF",and the gate circuit (DV) 77e-4 is selected. Consequently, the input ato the gate circuit (G) 77e-4 is energized to determine "+4" as thecorrection value for the white level value of the last scanning cycle.

In any other instance, depending upon whether an output is outputtedfrom the comparator (=F7 to FE?) 77c-1 or the comparator (-F6?) 77c-2 ofthe video signal comparator 77c, the corresponding gate circuit (DV)77e-0 or 77e-1 is selected so that the input β or γ(7) of the gatecircuit (G) 77e-1 or 77e-0 is energized. Consequently, same correctionas that described hereinabove with reference to FIG. 15 is performed.

In particular, the control method in the present example described aboveis characterized in that, when X"FF" as a white level successivelyappears in successive lines at a certain dot, it is recognized that asudden variation in white has occurred and thus such a correction isperformed that the white level value is raised progressively inaccordance with such sudden variation in white.

FIG. 17 shows a modification to the white level algorithm circuit 77shown in FIG. 16. In particular, referring to FIG. 17, the modifiedwhite level algorithm circuit 77 includes, for example, a read-onlymemory (ROM) 77h in place of the addition value selecting multiplexer77e and the addition circuit 77f of the white level algorithm circuit 77shown in FIG. 16. In particular, the output value (4 bits) of thecounting section (Count) 77d, the output (3 bits) of the video signalcomparator 77c and a white level value (8 bits) in the memory circuit72-1 or 72-2 obtained by scanning in the last scanning cycle are appliedas an address signal to the ROW 77h so that a white level valuecalculated and stored in advance in the ROM 77h is outputted from theROM 77h.

The white level value outputted in this manner is stored into theposition corresponding to the dot together with the value (Qa to Qd) ofthe counting section (Count) 77d and then used for calculation for whitelevel correction upon analog to digital conversion in a next line.

Then, also in this instance (in the case of FIG. 16 or 17), in such acase that paper sheets whose ground color is white have been read tillnow and blue print paper sheets of a different ground color are to beread subsequently, the white level value to be provided to the analog todigital conversion circuit 60 is varied in response to an instructionsignal from the MPU circuit 150 by the white level informationcorrection circuit 70 in a similar manner as described above. Inparticular, white level information stored in the memory circuit 72-1(or 72-2) is taken out and stored into the register 73-1 (or 73-2), andthen the output of the register 73-1 (or 73-2) is selected by theselection circuit 75a so that it is subsequently multiplied by m by thedata magnification variation circuit 74. Then, the output of the datamagnification variation circuit 74 is selected by the selection circuit75b and then processed by required processing by the white levelalgorithm circuit 77, and then the white level of the thus variedmagnification is stored into the other memory circuit 72-2 (or 72-1) byway of the selection circuit 75c. Then, the white level of the variedmagnification is used as a conversion reference of the analog to digitalconversion circuit 60.

Thereafter, so far as such blue print paper sheets are used, the whitelevel from the memory circuit 72-2 (or 72-1) is extracted, and now, theoutput of the memory circuit 72-2 (or 72-1) is inputted by way of theselection circuit 75b to the white level algorithm circuit 77. Then, theprocessing described above is performed subsequently by the white levelalgorithm circuit 77 shown in FIG. 16 or 17 so that the white levelvalue may have an appropriate value to update the white level.

Consequently, even in such a case that paper sheets whose ground coloris white have been read till now and blue print paper sheets of adifferent ground color are to be read subsequently, the white levelinformation correction apparatus copes with this sufficiently and canperform analog to digital conversion with a high degree of accuracy.Besides, by constructing the correction circuit for a white level from adigital circuit, analog parts in the entire circuit and patterns of aprinted circuit board of an image inputting device can be reduced to theminimum. Further, since correction of a white level is :performed bydigital processing, no oscillation occurs in a high frequency bandwhereas it often occurs with an analog comparator. Accordingly, also theadvantage that an increase in stability of operation and in efficiencyand certainty in designing can be achieved is obtained.

Further, in the case described above, since the digital circuit portionof the white level algorithm circuit 77 can be constructed only fromordinary logical OR and AND gate circuits, it can be included readilyinto a large scale integrated circuit (LSI).

Further, in the arrangement shown in FIG. 17, since the addition valueselecting multiplexer 77e and the addition circuit 77f describedhereinabove with reference to FIG. 15 are replaced, for example, withthe ROW 77h, the number of parts can be reduced, and higher densitymounting can be anticipated.

By the way, in the arrangement shown in FIG. 14, the plurality of (two)memory circuits 72-1 and 72-2 are used in order to store white levelinformation, and the memory circuits 72-1 and 72-2 are selectively usedusing a chip selection function of the address controller 72b. However,such an alternative arrangement as shown in FIG. 19 may be employedwherein a single memory circuit 72 is employed and an address of thememory circuit 72 is designated by the address controller 72b so as toselectively use a pair of different storage areas 72-11 and 72-12 of thememory circuit 72.

Also in this instance, for example, in such a case that paper sheetswhose ground color is white have been read till now and blue print papersheets of a different ground color are to be read subsequently, thewhite level value to be provided to the analog to digital conversioncircuit 60 is varied by the white level information correction circuit70 shown in FIG. 19 in a similar manner as described above. Inparticular, white level information stored in a certain storage area72-11 (or 72-12) of the memory circuit 72 is taken out and stored intothe register 73, and then the output of the register 73 is subsequentlymultiplied by m by the data magnification variation circuit 74. Then,the output of the data magnification variation circuit 74 is selected bythe selection circuit 75b and then processed by required processing bythe white level algorithm circuit 77 (refer to FIGS. 15 to 17), and thenthe white level of the thus varied magnification is stored into theother storage area 72-12 (or 72-11). Then, the white level of the thusvaried magnification is used as a conversion reference of the analog todigital conversion circuit 60.

Thereafter, so far as such blue print paper sheets are used, white levelinformation from the storage area 72-12 (or 72-11) is extracted, andnow, the output of the storage area 72-12 (or 72-11) is inputted by wayof the selection circuit 75b to the white level algorithm circuit 77.Then, the processing described above is performed subsequently by thewhite level algorithm circuit 77 shown in FIGS. 15 to 17 so that thewhite level value may have an appropriate value to update the whitelevel.

In this manner, also in this instance, the effects or advantagesachieved by the embodiment described above can be achieved. Further,since the single memory circuit 72 is employed and the storage area72-11 and 72-12 of the memory circuit 72 are selectively used bydesignating the address by means of the address controller 72b, there isno necessity any more of preparing a plurality of independent memorycircuits. Consequently, handling of the white level informationcorrection circuit 70 is facilitated.

Such another alternative arrangement as shown in FIG. 20 may be employedwherein a switching control circuit 78 is additionally provided forautomatically controlling selective switching of the selection circuit75b in accordance with a result of determination which is conducted bythe data magnification variation circuit 74 based on data obtained fromthe optical image reading unit 410 to determine whether white levelinformation should be varied by magnification variation.

In particular, the switching control circuit 78 includes a pair ofcomparators 78a and 78c and a counter 78b. In the switching controlcircuit 78, the output of the analog to digital conversion circuit 60 isfirst compared with a reference value from reference value setting means78d by the comparator 78a, and if the output of the analog to digitalconversion circuit 60 is higher than the reference value, the counter78b counts up by one. Further, the output of the counter 78b is comparedwith a dot reference value from dot reference value setting means 78e bythe comparator 78c. If the output of the analog to digital conversioncircuit 60 is higher by more than a predetermined line number than thereference value, then since the output of the counter 78b is higher thanthe dot reference value, a signal to instruct the selection circuit 75bto select the data magnification variation circuit 74 is developed fromthe comparator 78c. In response to the signal, the selection circuit 75bselects the output of the data magnification variation circuit 74, andconsequently, the white level is varied more suddenly than that byvariation by the white level algorithm circuit 77. Then, the variationis performed automatically based on data obtained from the optical imagereading unit 410 as described above. It is to be noted that, when theoutput of the analog to digital conversion circuit 60 is still higher bymore than the predetermined line number than the reference value evenafter the selection circuit 75b is switched to the data magnificationvariation circuit 74 side, the white level varied once is further variedby the data magnification variation circuit 74. In particular, if thewhite level is varied, for example, twice, then the white level isvaried to m² times.

It is to be noted that, in FIG. 20, a selection circuit 75e is furtherprovided. The selection circuit 75e selects the output of the whitelevel algorithm circuit 77 or predetermined value data (X"FF" whichcorresponds to the maximum value). In particular, a control signal VABSis supplied from the MPU circuit 150 to the selection circuit 75e sothat, in an initial state, the predetermined value data is outputtedfrom the selection circuit 75e, and thereafter, the output of the whitelevel algorithm circuit 77 is outputted from the selection circuit 75e.

In this manner, also with the white level information correction circuit70 shown in FIG. 20, the effects or advantages which can be achieved bythe embodiment described above can be achieved. Further, since it isdetermined by the data magnification variation circuit 74 based on dataobtained from the optical image reading unit 410 whether or not whitelevel information should be varied by magnification variation and thenselective switching of the selection circuit 75b is automaticallycontrolled in accordance with a result of the determination, even whenpaper sheets used are changed, the white level can be automaticallyvaried rapidly.

It is to be noted that, while, in the several arrangements describedabove, the white level is varied for each picture element, it need notnecessarily be corrected for each picture element, but may naturally becorrected, for example, for each line.

Referring back to FIG. 2, an image signal after digital conversion bythe analog to digital conversion circuit 60 is transferred to the imageprocessing section 68A or 68B for next image processing such as, forexample, emphasis processing to emphasize the contrast between white andblack or "dither processing: binary digitization processing" for a netpoint image (which is constituted from a large number of fine dots; dotimage) such as a photograph image.

3-3. Outputting Section and Output Control Circuit

In each of the image data processing systems D1 and D2, informationdigitized by the analog to digital conversion circuit 60A or 60B issent, after it is processed by emphasis processing and/or binarydigitization processing by the image processing section 68A or 58B, tothe outputting section 90 as seen from FIG. 2, and paper front face dataand paper rear face data are transferred from the outputting section 90to the host computer (not shown).

Referring now to FIG. 21, the outputting section 90 includes a latchcircuit 91, a DRAM (buffer storage apparatus) 92, a rear face memorycontrol section 93, a read data buffer 94, a rear face timing generationsection 95 and a selection circuit 96.

The latch circuit 91 latches paper front face data VDA and front facetiming signals VGA, HGA and VCLKA from the image data processing systemD1 for processing paper front face data and notifies to the outputcontrol circuit 100 that the paper front face data and the surfacetiming signals have been latched by the latch circuit 91. It is to benoted that a flip-flop may be used for the latch circuit 91.

The timing signal VGA is a gate signal in a horizontal direction(direction of a line; main scanning direction), and the timing signalHGA is a gate signal in a vertical direction (paper transportingdirection; sub-scanning direction). One bit of a picture element in oneline on the front face of a paper sheet can be extracted using thetiming signal VGA and the timing signal HGA. Further, the timing signalVCLKA is a clock signal which defines the transfer rate of front facedata.

The DRAM 92 is a memory circuit for storing paper rear face data VDB.Storage and read-out control of the DRAM 92 is performed by the rearface memory control section 93. In particular, the rear face memorycontrol section 93 is constructed as a DMAC (dynamic memory accesscontroller) and stores paper rear face data VDB sent thereto into theDRAM 92. After paper front face data VDA for one sheet are sent, therear face memory control section 93 controls the DRAM 92 so that,between successive storing operations of paper rear face data VDB intothe DRAM 92, the paper rear face data VDB are read out from the DRAM 92(in this instance, the paper rear face data VDB are read out in units ofone bit).

It is to be noted that all data for one full paper sheet from the lateroperating image reading unit 14 need not necessarily be stored into theDRAM 92, and actually, those data obtained after outputting of data forone full paper sheet from the first operating image reading unit 412 iscompleted until all information stored in the DRAM 92 is sent out arestored. In particular, data from the later operating image reading unitare stored for a period of time after outputting of data for one fullpaper sheet from the other first operating image reading unit iscompleted until it becomes possible to pass and output data from thelater operating image reading unit through and from the rear face memorycontrol section 93. This can decrease the memory capacity.

It is a matter of course that data from the later operating imagereading unit 414 may all be stored for one full paper sheet into theDRAM 92. This facilitates memory control.

The read data buffer 94 temporarily stores, between successive storingoperations of paper rear face data VDB into the DRAM 92, paper rear facedata VDB partially read out from the DRAM 92 and produces arranged datato be sent. Where the read data buffer 94 is provided in this manner,data can be read out little from the DRAM 92 while giving priority towriting into the DRAM, and consequently, the data transfer time can bereduced.

It is to be noted that the rate at which data are read out from the DRAM92 and the read data buffer is set equal to twice the writing rate, thatis, the transfer rate of front face data to the host computer.

The rear face timing generation section 95 generates rear face timingsignals VGB, HGB and VCLKB. Also in this instance, the timing signal VGBis a gate signal in a horizontal direction (direction of a line; mainscanning direction), and the timing signal HGB is a gate signal in avertical direction (paper transporting direction; sub-scanningdirection). One bit of a picture element in one line on the rear face ofa paper sheet can be extracted using the timing signal VGB and thetiming signal HGB. Further, the timing signal VCLKB is a clock signalwhich defines the transfer rate of front face data. In this instance,the rate of the rear face timing signal VCLKB is set to twice that ofthe front face timing signal VCLKA. Due to the rate and also due to thedata read-out data rate from the DRAM 92 and the read data buffer 94,rear face data are transferred at the rate equal to twice that of frontface data.

The selection circuit 96 receives a control signal from the outputcontrol circuit 100 and selectively outputs paper front face data orpaper rear face data in accordance with the control signal. In thisinstance, after paper front face data are transferred for one full papersheet, the data to be outputted are switched so that paper rear facedata are thereafter transferred for one complete paper sheet.

It is to be noted that the output control circuit 100 is switched to thepaper front face data side in response to paper leading end detectioninformation but is switched to the paper rear face data side in responseto paper trailing end detection information. Such detection of a leadingend or a trailing end of a paper sheet will be hereinafter afterdescribed.

Therefore, it is considered that the outputting section 90 includes thestorage means (DRAM) 92 for storing data (paper rear face data) fromthat one of the first optical image reading unit 412 and the secondoptical image reading unit 414 which serves as a later operating imagereading unit (in the present example, the second optical image readingunit 414) from which paper image information is read out later than fromthe other image reading unit.

Also it is considered that the outputting section 90 further includesfirst data transfer means (the latch circuit 91 and the selectioncircuit 96) for successively transferring, by way of a data transferline, paper front face data from that one of the first optical imagereading unit 412 and the second optical image reading unit 414 whichserves as a first operating image reading unit (in the present example,the first operating image reading unit 412) from which paper imageinformation is read out first, and second data transfer means (the rearface memory control section 93, the rear face timing generation section95 and the selection circuit 96) for successively transferring, by wayof another data transfer line, after paper front face data from thefirst operating image reading unit 412 are transferred by the first datatransfer means, paper rear face data from the later operating imagereading unit 414 stored in the storage means 92 at a rate (in thepresent example, at the twice rate) higher than the data transfer rateby the first data transfer means.

Further, it is also considered that the outputting section 90 furtherincludes auxiliary storage means (the read data buffer 94) for storingpartial paper image information read out from the storage means 92between successive writing operations of data into the storage means(DRAW) 92.

It is to be noted that the reason why paper rear face data are sent at arate twice that of paper front face data is that it is desired thatpaper rear face data be transferred to the host computer side before thepaper sheet 40 whose front face and rear face have been read isthereafter discharged to the stacking mechanism 500. This is because, ifa paper sheet is discharged to the stacking mechanism 500, thentransportation of a new paper sheet is started and reading of data ofthe paper sheet is started. In other words, paper rear face data aretransferred at the rate twice that of paper front face data because itis desired to complete transfer of rear face data before transportationof a next paper sheet is started. Accordingly, naturally the value twicemay possibly be varied depending upon the length of the paper transportpath, the paper transport velocity or the like of the image readingapparatus.

Accordingly, the outputting section 90 operates in such a manner asillustrated in FIG. 22.

Referring to FIG. 22, since the selection circuit 96 is initiallyswitched to the paper front face data side, paper front face data aretransferred by through-transfer (step A1). Thereafter, when the signalVGA becomes negated, that is, when transfer of the front face data iscompleted, the route of "YES" is taken at step A2, and then theselection circuit 96 is switched to the paper rear face data side (stepA3). Then, at step A4, paper rear face data are read out from the DRAM92 and transferred at a high rate to the read data buffer 94 (step A5).Then, this operation is repeated until the DRAM (image sensor) 92becomes emptied (step A6).

Due to the construction described above, data (paper front face data)from the first operating image reading unit 412 from between the firstoptical image reading unit 412 and the second optical image reading unit414 from which paper image information is to be read out first are firsttransferred successively by way of a data transfer line, and data (paperrear face data) from the later operating image reading unit 414 frombetween the first optical image reading unit 412 and the second opticalimage reading unit 414 from which paper image information is to be readout later are temporarily stored into the DRAM 92 and, after the datafrom the first operating image reading unit 412 are transferredcompletely, the stored data from the later operating image reading unit414 are successively transferred at a rate higher than the transfer rateof the data from the, first operating image reading unit 412 by way ofanother data transfer line. Consequently, the following advantages canbe obtained.

In particular, even if image reading by the later operating imagereading unit 414 is started before image reading by the first operatingimage reading unit 412 is completed, data within the overlapping periodcan be held with certainty. Besides, data from the later operating imagereading unit 414 from which data are transferred later can betransferred rapidly to the host computer side.

Accordingly, even where the image reading units 412 and 414 are disposedin the proximity of the paper transport path in order to achieveminimization, reduction in weight and compaction of the apparatus, dataof the front and rear faces of a paper sheet can be transferred to thehost computer side before the paper sheet is discharged to the stackingmechanism 500. Consequently, even if paper sheets are successivelytransferred at a high speed while achieving minimization, reduction inweight and compaction of the apparatus, data of the front and rear facesof each paper can be read and transferred to the host computer sidesatisfactorily.

By the way, the output control circuit 100 includes, as describedhereinabove, the paper leading end detection circuit 450 for detectingpaper leading end information and the paper trailing end detectioncircuit 451 for detecting paper trailing end information.

The paper leading end detection circuit 450 and the paper trailing enddetection circuit 451 have a same circuit construction and eachincludes, as shown in FIG. 23, magnitude comparators 131, 138 and 139, amultiplexer 132, registers 133, 134, 135 and 141, adders 136 and 137,and an OR gate 140.

Due to the construction, a video signal (paper front face data) from theimage reading unit 412 is inputted to an input terminal A of themagnitude comparator 131. The magnitude comparator 131 thus compares thevideo signal from the image reading unit 412 with the output of theregister 133 which is inputted to the magnitude comparator 131 by way ofanother input terminal B. In this instance, if the video signal ishigher, then the video signal is outputted from the multiplexer 132 sothat it is latched by the register 133. On the contrary if the output ofthe register 133 is higher, then the output of the register 133 isoutputted from the multiplexer 132 so that it is latched by the register133. Such comparison in magnitude is repeated. Consequently, at the endof the line, a maximum value (peak value) of the line is latched in theregister 133.

Therefore, it can be understood that the magnitude comparator 131, themultiplexer 132 and the register 133 construct one-line peak valuedetection means for detecting a peak value in one line along thedirection perpendicular to the paper transporting direction based on animage signal from an optical image reading unit.

Further, a clock BB (this clock BB is developed once for one line at theend of the line) causes the register 134 to latch a maximum value (peakvalue) in one line latched in the register 133 and simultaneously causesthe register 135 to latch a maximum value (peak value) of the last line.Consequently, the registers 133 and 134 construct a shift register forstoring both of a current peak value detected by the one-line peak valuedetection value and a past peak value in one line detected prior to thecurrent peak value.

Meanwhile, the register 135 is constructed as storage means for storinga past peak value in one line detected prior to a current peak valuedetected by the one-line peak value detection means.

Thereafter, +n (n is a natural number) is added to a maximum value (peakvalue) of a preceding line by the adder 136, and -n is added to (thatis, n is subtracted from) the maximum value by the adder 137. Then, theoutput of the adder 136 and the maximum value (peak value) of thecurrent line from the register 134 are compared with each other by themagnitude comparator 138, and the output of the adder 137 and themaximum value (peak value) of the current value from the register 134are compared with each other by the magnitude comparator 139.

Then, if the maximum value of the current line is higher than the sum ofthe maximum value of the preceding line and n, the magnitude comparator138 outputs "1", but if the maximum value of the current line is lowerthan the difference of n from the maximum value of the preceding line,the magnitude comparator 139 outputs "1". Consequently, if the maximumvalue of the current line is higher than the sum of the maximum value ofthe preceding line and n or lower than the difference of n from themaximum value of the preceding line, then the OR gate 140 outputs "1".

Then, the output of the OR gate 140 is latched by the register 141 whichoperates in response to a clock AA (the clock AA is outputted once forone dot) in order to prevent fluctuation, and the output of the register141 is used as a paper leading end detection signal or a paper trailingend detection signal. Then, such paper leading or trailing end detectionsignal is used as an interruption requesting signal (IRQ) to the MPUcircuit 150.

Consequently, it can be seen that the magnitude comparators 138 and 139cooperatively construct comparison means for comparing a current peakvalue detected by the one-line peak value detection means and a pastpeak value from the storage means with each other and outputting aresult of the comparison as a paper leading or trailing end detectionsignal.

Meanwhile, the adder 136 constructs addition means for adding apredetermined value (n) to a past peak value from the register (storagemeans) 135. Thus, the magnitude comparator (comparison means) 138 isconstructed so as to compare a current peak value detected by theone-line peak value detection means and an addition correction past peakvalue from the adder 136 with each other and output a result of thecomparison as a paper end detection signal.

Further, the adder 137 constructs subtraction means for subtracting apredetermined value (n) from a past peak value from the register(storage means) 135. Thus, the magnitude comparator (comparison means)139 is constructed so as to compare a current peak value detected by theone-line peak value detection means and a subtraction correction pastpeak value from the adder 137 with each other and output a result of thesubtraction as a paper leading or trailing end detection signal.

Meanwhile, the magnitude comparator 138 constructs first comparisonmeans for comparing a current peak value detected by the one-line peakvalue detection means and an addition correction past peak value fromthe adder (addition means) 136 with each other. The magnitude comparator139 constructs second comparison means for comparing a current peakvalue detected by the one-line peak value detection means and asubtraction correction past peak value from the adder (subtractionmeans) 137 with each other. The OR gate 140 constructs outputting meansfor outputting, when a paper end detection signal is outputted from atleast one of the first comparison means and the second comparison means,the paper end detection signal as a paper end detection signal.

Further, the register 141 constructs latching means for latching theoutputs of the comparison means.

It is to be noted that FIG. 24 illustrates signal waveforms (time chart)at several locations of the circuit shown in FIG. 23.

The leading end or the trailing end of a paper sheet is detected in sucha manner as described above. The paper leading end detection circuit 450detects the leading end of a paper sheet based on a paper end detectedfor the first time, and when the MPU circuit 150 receives such paperleading end detection signal as an interruption requesting (IRQ) signalfrom the paper leading end detection circuit 450, the MPU circuit 150develops, in response to the interruption requesting (IRQ) signal, acommand signal to read the front face of the paper sheet. As a result,also the selection circuit 96 is switched to the paper front face dataside.

Meanwhile, the paper trailing end detection circuit 451 detects thetrailing end of the paper sheet based on a paper end detected for thesecond time, and when the MPU circuit 150 receives such paper trailingend detection signal as an interruption requesting (IRQ) signal from thepaper trailing end detection circuit 451, the MPU circuit 150 develops,in response to the interruption requesting (IRQ) signal, a commandsignal to read the rear face of the paper sheet. As a result, also theselection circuit 96 is switched to the paper rear face data side.

Therefore, the outputting section 90 is constructed as image signalprocessing means for processing image signals obtained by the opticalimage reading units in response to a result of detection by the paperend detection apparatus.

Accordingly, if the paper leading end detection circuit 450 and thepaper trailing end detection circuit 451 of such circuit construction asdescribed above are employed, the leading end and the trailing end of apaper sheet can be detected with certainty with a common circuitconstruction and with a simple construction. Consequently, readingtimings of paper front face data and paper rear face data or readingswitching timings between them can be controlled precisely irrespectiveof the type of a paper sheet being transported. As a result, it iscomparatively simple for the image reading apparatus to allow papersheets of various sizes to be transported to read information on them.

It is to be noted that, while any of the leading end and the trailingend of a paper sheet can be detected by the construction shown in FIG.23, where the ground color of a paper sheet 40 is brighter than thecolor of the backing member provided on the paper transport path 310, ifit is intended to only detect the leading end of the paper sheet 40,then the adder 137, the magnitude comparator 139 and the OR gate 140 canbe omitted. Similarly, if it is intended to only detect the trailing endof the paper sheet 40, then the adder 136, the magnitude comparator 138and the OR gate 140 can be omitted. On the contrary, where the groundcolor of a paper sheet 40 is darker than the color of the backing memberprovided on the paper transport path 310, if it is intended to onlydetect the leading end of the paper sheet 40, then the adder 136, themagnitude comparator 138 and the OR gate 140 can be omitted. Similarly,if it is intended to detect only the trailing end of the paper sheet 40,then the adder 137, the magnitude comparator 139 and the OR gate 140 canbe omitted.

4. Control System

4-1. Operation Panel

Referring now to FIG. 31, the operation panel 920 has provided thereonvarious indication lamps including a power source input indication lamp922A, a reading enable indication lamp 922B and a check lamp 922C, and aliquid crystal display unit 922D for displaying various information bycharacters. The liquid crystal display unit 922D suitably displays, forexample, information of an operation input, an error message, and soforth.

The operation panel 920 further has provided thereon a plurality ofautomatic reading mode setting switches 924A and 924B each serving asinsertion mode selection means for selectively setting one of aplurality of (two including a mode 1 and a mode 2 here) automaticreading modes, a manual insertion setting switch 924C serving asinsertion mode selection means for setting a manual insertion mode, astart switch 924D for starting the image reading apparatus, and a stopswitch 924E for stopping the image reading apparatus. In order to startthe apparatus, one of the mode 1, the mode and the manual insertion modeis set, and then the start switch 924D will be operated.

The operation panel 920 further has provided thereon an original sizeinputting switch 924F, a reading concentration setting switch 924G, areading density setting switch 924H, a landscape switch 924J, a halftone (half tone) setting switch 924K, and the original selection switch(paper reading selection means) 924L. The original selection switch 924Lis a switch by which it can be set whether both face reading of anoriginal should be performed or one face reading only of the front faceor the rear face should be performed.

4-2. Construction of the Control System

FIG. 3 schematically shows the mechanical components described above andcontrol sections for controlling the mechanical components. Referring toFIG. 3, a control section 930 includes a mechanical section controlmeans 932 including a control circuit for controlling mechanicaloperations of the mechanical components, and image reading systemcontrol means 934 including a control circuit for controlling operationof the image reading system. A pair of power source adjustment sections940A and 940B for transforming an external power source to requiredvoltages are connected to the image reading system control means 934.

The mechanical section control means 932 controls operation of thetransport systems (that is, the paper supply mechanism 200, the papertransport mechanism 300, the paper stacking mechanism 500 and so forth)and the heater of the lamp unit and an invertor of the fluorescent lampin accordance with an instruction signal received by way of the imagereading system control means 934 and detection information from thevarious sensors of the mechanical components. The mechanical sectioncontrol means 932 also controls operation of a cooling fan 936 for thecontrol section 930 itself. The paper supply hopper position controlmeans (motor control means) 280, the pick clutch control means 250serving as paper supply roller driving mechanism control means, theseparation clutch control means 858 and the roller driving mechanismcontrol means 350 described hereinabove are included in the mechanicalsection control means 932.

The image reading system control means 934 controls operation of CCDdriver units of the first optical image reading unit 412 and the secondoptical image reading unit 414, a video circuit and a rear face readingboard 944 and outputting to an outputting interface board 938 inresponse to setting information of the operation panel 920 andinformation from the mechanical section control means 932. The imageinformation extraction control means 440, the paper leading enddetection circuit 450, the paper trailing end detection circuit 451 andthe discrimination mark image erasure means 460 described hereinaboveare provided in the image reading system control means 934.

Where an endorser (endorsing printer) 942 is provided in the proximityof the terminal end of the paper transport path 310 as shown in FIG. 7,also a driver for the endorser 942 is controlled by the image readingsystem control means 934 as seen from FIG. 3. Also where an extensionmemory board and/or an auxiliary printed circuit board (IPC-2) areprovided, they are controlled by the image reading system control means934.

4-3. Operation

Operations of the hopper motor 242, the pick clutch 238, the separationclutch 854 and the transport motor 342 and control by the imageinformation extraction control means 440 proceed, for example, in such amanner as illustrated in time charts of FIGS. 25 to 30.

First, control of the hopper motor 242 will be described. Upon startingof the control, control of an initialization mode is performed as seenfrom FIG. 25. In particular, in response to an operation startinginstruction (that is, a control starting instruction) for the imagereading apparatus such as, for example, throwing in of a power source tothe apparatus, the hopper motor 242 is rotated in a direction to lowerthe hopper table 212. Then, when the hopper table 212 comes to itslowermost position, the bottom sensor 622 switches from an off-state(open) to an on-state (closed), and the hopper motor 242 stops inresponse to such detection signal of the bottom sensor 622. Naturally,the control is not performed if, upon reception of the control startinginstruction, the hopper table 212 is already at the lowermost positionand the bottom sensor 622 is in an on-state (closed).

The control of the hopper motor 242 after this is different between anautomatic reading mode and the manual insertion mode in response tosetting information of the switches.

In particular, if paper sheets 42 are accommodated into the hopper table212 and a switch operation (depression of the start button) for anautomatic reading mode is performed, then the hopper motor 242 isrotated in a direction to raise the hopper table 212 as seen from FIG.26. Then, when the top of the paper sheets 40 in the hopper table 212rises from a position (bottom position) corresponding to the lowermostposition of the hopper table 212, whereupon the hopper empty sensor 610is turned on ("presence of a paper sheet"), to a prescribed height atwhich the paper supply sensor 612 is turned on ("presence of a papersheet").

When the hopper table 212 is raised by a little distance after the papersupply sensor 612 is turned on, the hopper motor 242 is stopped.Thereafter, image reading is performed while paper supplying andtransporting operations are performed. During the process, as the papersheets 40 are supplied, the height of the top of the stack of papersheets 40 decreases. Consequently, the paper supply sensor 612 is turnedoff finally, and in response to this, the hopper motor 242 is rotated inthe direction to raise the hopper table 212.

Then, as the height of the top of the stack of paper sheets 40 in thehopper table 212 rises again, it finally reaches the prescribed height,whereupon the paper supply sensor 612 is turned on ("presence of a papersheet"). While such a sequence of operations as described above isrepeated to control the height of the top of the paper sheets within afixed range, image reading operation is performed together with papersupplying and transporting operations.

On the other hand, if a switch operation for the manual insertion mode(depression of the manual insertion button) is performed, then thehopper motor 242 is rotated in the direction to raise the hopper table212 as seen from FIG. 27. Then, when the hopper table 212 is raiseduntil the height of the top end thereof comes to a prescribed height,then the paper supply sensor 612 is turned on ("presence of a papersheet"). When the hopper table 212 is further raised a little after thepaper supply sensor 612 is turned on, the hopper motor 242 is stopped.Thereafter, the hopper motor 242 is kept stopped and the hopper table212 keeps the position. Then, manual insertion of a paper sheet isperformed as can be seen also from an on/off condition of the hopperempty sensor 610.

Subsequently, operations of the pick clutch 238, the separation clutch854 and the transport motor 342 and control by the image informationextraction control means 440 will be described together with operationof the hopper motor 242. Referring to FIG. 28, paper sheets 40 are firstaccommodated into the paper supply hopper 210 and a start command toinstruct starting of image reading is developed (point T1). At thisinitial stage, since the paper supply hopper 210 is not at the papersupply position, the paper supply sensor 612 is in an off-state. Thehopper empty sensor 610 also provides a signal indicating absence of apaper sheet.

Since the paper supply sensor 612 is in an off-state, the hopper motor242 is rendered operative to raise the paper supply hopper 210 to thepaper supply position (point T2). Consequently, the paper supply sensor612 is turned on. As a result, the hopper motor 242 is stopped, and thepick clutch 238 and the separation clutch 854 are engaged. Thereafter,the transport motor 342 is started (point T3) after a small time lag (30ms in the example shown) until the pick clutch 238 and the separationclutch 854 are engaged firmly. By the operation of the transport motor342, the pick rollers 220 and the separation roller 820 are rotated byway of the pick clutch 238 and the separation clutch 854 to supply andtransport a first paper sheet.

The transport motor 342 can be selectively set to one of a low speedmode of a velocity V₁ (for example, 12 to 13 cm/s), a high speed mode ofanother velocity V₂ (for example, about 50 cm/s) and an intermediatespeed mode (mid speed mode) of an intermediate velocity between them.For the first paper sheet upon starting of paper supply, the transportmotor 342 operates in the low speed mode. Accordingly, also thetransportation speeds of the pick rollers 220 and the separation roller820 are low.

When the leading end of the paper sheet being transported in this mannerpasses the transport sensor 614, the transport sensor 614 detects thisand is turned on (point T4), and the pick clutch 238 is disengaged. Atthis point of time, the paper sheet is already at a position at which itcan be driven by the separation roller 820, and consequently, the papersheet is thereafter driven by the separation roller 820.

Then, when the leading end of the paper sheet being transported passesthe transport sensor 616, the transport sensor 616 detects this and isturned on (point T5), and the separation clutch 854 is disengaged. Atthis point of time, the paper sheet is already at a position at which itcan be driven by the transport roller 320, and consequently, the papersheet is thereafter driven by the transport roller 320. Thereafter, thepaper sheet is successively driven by the succeeding transport rollers322 to 328. At the point of time T5, since the transport motor 342 is inthe low speed mode, the transportation velocity of the transport roller320 itself is low.

The transport sensor 616 serves also as a sensor for detecting a readingtiming, and when the passage of the leading end of the paper sheet isdetected by the transport sensor 616, a read command is developed inresponse to the detection (point T6). Upon reception of the readcommand, the transport motor 342 is accelerated from the low speed mode(velocity V₁) to the high speed mode (velocity V₂). Accordingly, alsothe speed of rotation of the transport rollers 320 to 328, that is, thetransportation speed, increases until high speed transportation isreached.

Then, at a point of time T7 after lapse of a predetermined time t₃ afterthe leading end of the paper sheet passes the transport sensor 616, thefirst optical image reading unit 412 for reading information of thefront face of the paper sheet is put into a reading condition.Thereafter, at another point of time T8 after lapse of anotherpredetermined time t₄ after the leading end of the paper sheet passesthe transport sensor 616, the second optical image reading unit 414 forreading information on the rear face of the paper sheet is put into areading condition. In particular, each video gate (not shown) of thevideo circuit board 438 is put into an on-state.

It is to be noted that the predetermined times t₃ and t₄ are timesrequired for a paper sheet to pass from the transport sensor 616 to thereading points 412A and 414A of the optical image reading units 412 and414, respectively, and are given, from the distances L₁ and L₂ from thetransport sensor 616 to the reading points 412A and 414A and thetransportation speed V₂ by the transport roller 320, by the followingequations, respectively;

    t.sub.3 =L.sub.1 /V.sub.2, t.sub.4 =L.sub.2 /V.sub.2

During such image reading (at points of time T9 and T10), the transportsensors 614 and 616 are switched from on to off when the trailing end ofthe paper sheet passes the transport sensors 614 and 616, respectively.

Then, in each of the optical image reading units 12 and 414, when a timet₅ required for image reading passes (point T11 or T12), the video gateis switched from on to off, thereby completing reading (Read Complete).It is to be noted that the time t₅ is given as a product between thereading line number and the integration time (t₅ =reading linenumber×integration time).

In this manner, while the first paper sheet is transported in the highspeed mode by the transport rollers 320 to 328, image reading of thefront face and the rear face of the paper sheet is performed by theoptical image reading units 412 and 414, respectively, and thereafter,the paper sheet is driven by the paper transport roller 328 and stackedinto the paper stacker 510.

After reading of the first paper sheet is completed, a start command isdeveloped immediately, and in response to the start command,transportation and reading of a second paper sheet are started. In theoperation for the second or following paper sheet, the image readingapparatus operates in such a manner as illustrated in FIG. 29.

In particular, in the present example, since the paper supply hopper 210is at the paper supply position (that is, the paper supply sensor 612 isin an on-state) when the start command is instructed (point T13), thepick clutch 238 and the separation clutch 854 are engaged simultaneouslywith the instruction of the start command. Since the transport motor 342continues to operate in the high speed mode, the pick roller 220 and theseparation roller 820 are rotated at a comparatively high speed due tothe engagement of the clutches 238 and 864 to transport the second papersheet. Naturally, in this instance, also the transport rollers 320 to328 are being rotated by the transport motor 342.

Thereafter, transportation and reading of the second paper sheet areperformed substantially in a similar manner to the first paper sheet.However, in transportation and reading of the second or following papersheet, since the transport motor 342 is operating in the high speed modefrom the beginning, the transport motor 342 is controlled to temporarilylower the speed thereof at a point of time when the main element fordriving the paper sheet changes over from the separation roller 820 tothe transport roller 320, different from the transportation and readingof the first paper sheet.

In particular, when the leading end of the second paper sheet which issupplied and transported at a comparatively high speed by the pickroller 220 and the separation roller 820 passes the transport sensor614, the transport sensor 614 detects this and is turned on (point T15).Consequently, the pick clutch 238 is disengaged and the paper sheet isthereafter driven by the separation roller 820.

Then, when the leading end of the second paper sheet passes thetransport sensor 616, the transport sensor 616 detects this and isturned on (point T19), and the separation clutch 854 is disengaged.Around the point of time T19 (between the points of time T17 to T20),the speed of the transport motor 342 is reduced temporarily from thehigh speed mode to the intermediate speed mode.

Such speed reduction control is started at a point of time T16 when arequired time elapses after the transport sensor 614 is turn on (at apoint of time before the leading end of the paper sheet passes thetransport sensor 616) and is performed by holding, after the point oftime T17 at which the speed drops to an intermediate speed, theintermediate speed till a point of time T20 at which a predeterminedtime (for example, 50 ms) elapses after the point of time T17.

Due to the speed reduction control, when the main element for drivingthe paper sheet changes over from the separation roller 820 to thetransport roller 320, the transportation speed of the separation roller820 and the transport roller 320 is suppressed, and consequently,changing over from the separation roller 820 to the transport roller 320proceeds smoothly. This reduces a cause of a trouble such as paperjamming.

Within the period, a read command is developed (point T18), andsimilarly as in transportation of the first paper sheet, the firstoptical image reading unit 412 for reading information of the front faceof a paper sheet is put into a reading condition at a point of time T21at which the predetermined time t₃ elapses after the leading end of thepaper sheet passes the transport sensor 616. Then, at another point oftime T22 when the predetermined time 14 elapses after the leading end ofthe paper sheet passes the transport sensor 616, the second opticalimage reading unit 414 for reading information of the rear face of apaper sheet is put into a reading condition. In particular, each videogate (not shown) of the video circuit board 438 is put into an on-state.It is to be noted that the predetermined times t₃ and t₄ mentioned aboveare given similarly as described hereinabove.

During such image reading, the transport sensors 614 and 616 are changedover from an on-state to an off-state (points T23 and T24) as thetrailing end of the paper sheet passes the transport sensors 614 and616, respectively.

Then, in each of the optical image reading units 412 and 414, the videogate is changed over from an on-state to an off-stage to complete thereading (Read Complete) when the time t₅ required for image readingelapses. Also the time t₅ is given similarly as described hereinabove.

In this manner, while the second or following paper sheet is transportedin the high speed mode by the transport rollers 320 to 328, imagereading of the front face and the rear face of the paper sheet isperformed by the optical image reading units 412 and 414, respectively,and thereafter, the paper sheet is driven by the paper transport roller328 and the paper discharge roller and stacked into the paper stacker510.

If the paper supply sensor 612 is turned off as a result of reduction inquantity of the paper sheets 40 in the paper supply hopper 210 (pointT14 in FIG. 29), then the hopper motor 242 is rendered operative at apoint of time (T27) at which the operations of the pick roller 220 andthe separation roller 820 and the speed reduction control of thetransport motor 342 are completed to raise the paper supply hopper 210to the paper supply position (point T2). Such height control of thepaper supply hopper 210 is performed each time the paper supply sensor612 is turned off as a result of reduction in quantity of the papersheets 40 while the paper supplying and transporting operations areperformed.

Then, when the paper sheets 40 in the paper supply hopper 210 arereduced in quantity until the paper supply hopper 210 becomes empty, thehopper empty sensor 610 changes over from an off-state ("paper present")to an on-state ("paper absent") (point T28) as seen from FIG. 30, andthen the transport sensor 616 changes over from an on-state ("duringpaper passage") to an off-state ("completion of paper passage") (pointT29). Thereafter, the video gate of the second optical image readingunit 414 on the downstream side of the transport path is changed overfrom an on-state to an off-state and simultaneously the read command ischanged over from an on-state to an off-state (point T30), and then thedischarge sensor 618 changes over from an on-state ("during paperpassage") to an off-state ("completion of paper passage") (point T31).The power supply to the transport motor 342 is cut to stop the transportmotor 342 after lapse of a predetermined time t₈ after the dischargesensor 618 changes over to an off-state. The predetermined time t₈corresponds to a time within which a paper sheet 40 is transported fromthe discharge sensor 618 to the stacker 500.

It is to be noted that, if a paper sheet to be read requires imagereading of only one face thereof and it is intended to read, forexample, only the front face of the paper sheet, when reading of thevideo gate of the first optical image reading unit 412 in FIGS. 28 and29 comes to an end, it is determined that reading for the paper sheet iscompleted (Read Complete), and next control is started immediately.

Since transportation and image reading of paper sheets is performed inresponse to the hopper empty sensor 610, the paper supply sensor 612,the transport sensors 614 and 616 and the discharge sensor 618 in thismanner, the image reading operation can be performed appropriately inaccordance with a transportation condition of a paper sheet, which issuitable to high speed image reading. Further, if paper jamming (paperjamming) should occur intermediately of the paper transport path, thiscan be detected promptly and the operation of the image readingapparatus can be stopped immediately.

Further, since the control timings by the roller driving mechanismcontrol means 350 and the image information extraction control means 440are synchronized with each other, even if the processing speed for imagereading is increased, the paper transportation operation and the imagereading operation can be performed with certainty.

Furthermore, since reading of information of the front face of a papersheet 40 is performed optically by the first optical image reading unit412 and reading of information of the rear face of the paper sheet 40 isperformed optically by the second optical image reading unit 414,reading of image information on the opposite faces of the paper sheet 40can be performed rapidly, and the processing speed of a double-sideoriginal is improved significantly.

Further, with the image reading apparatus of the present embodiment, thefollowing advantages can be achieved due to its structuralcharacteristics.

In particular, since the paper transport path 310 connected to the papersupply mechanism 200 is constituted from the inclined transport path 312and the paper reversing transport path 314 without involving ahorizontal transport path, the paper transport path 310 requires acomparatively small depthwise space, and accordingly, there is anadvantage in that the image reading apparatus can be reduced in size asmuch. Further, there is another advantage in that a paper sheet can betransported rapidly from the paper supply mechanism 200 to the stackermechanism 300 and image reading can be performed at a high speed.Naturally, the reduction in space allows an increase in size of thepaper sheet hopper or the paper stacker, which allows reading of a papersheet of a greater size.

By the way, referring back to FIG. 2, analog video signals from the CCDarrays 436AA and 436AB of the image reading units 412 and 414 areamplified by the amplification circuits 64A and 64B, respectively, andthe analog video signals of the outputs of the amplification circuits64A and 64B in portions (bits) in which, for example, the photosensitiveportions of the CCD arrays 436AA and 436AB are masked are sampled andheld by the black level setting circuits (sample hold circuits) 71A and71B and are connected as reference signals for a black level to thelower limit sides (VRB) of the analog to digital conversion circuits 60Aand 60B, respectively. For a reference signal for a white level, asignal obtained by digital to analog conversion of a white level valueof each bit of each line obtained by scanning in the last scanning cycleand stored in the memory circuit 72-1 or 72-2 by the digital to analogconversion circuit 62A or 62B is used and connected to the upper limitside (VRT) of the analog to digital conversion circuit 60A or 60B.

Consequently, the analog to digital conversion circuit 60A or 60Boutputs a multiple value digital signal on the scale of 256 gradationsbetween the reference level (VRT) for white and the reference level(VRB) for black. In this instance, for the reference level for white, ananalog value of a white level produced with reference to a white levelobtained by scanning of the image in the last scanning cycle is used,and for the reference value for black, an analog value at a dot at whichthe photosensitive element of the CCD array 436AA or 436AB is masked isused.

It is to be noted that, in this instance, for example, in such a casethat paper sheets whose ground color is white have been read till nowand blue print paper sheets of a different ground color are to be readsubsequently, the white level value to be provided to the analog todigital conversion circuit 60 is varied in response to an instructionsignal from the MPU circuit 150 by the white level informationcorrection circuit 70. In particular, as seen from FIGS. 14 to 20, whitelevel information stored in the memory circuit 72-1 (or 72-2) or thestorage area 72-11 (or 72-12) is taken out and stored into the register73-1 (or 73-2) or 73, and then the output of the register 73-1 (or 73-2)or 73 is multiplied by m by the data magnification variation circuit 74.Then, the output of the data magnification variation circuit 74 isselected by the selection circuit 75a and then processed by requiredprocessing by the white level algorithm circuit 77, and then the whitelevel of the thus varied magnification is stored into the other memorycircuit 72-2 (or 72-1) or the other storage area 72-12 (or 72-11) by wayof the selection circuit 75c. Then, the white level of the variedmagnification is used as a conversion reference of the analog to digitalconversion circuit 60.

Thereafter, so far as such blue print paper sheets are used, the whitelevel from the memory circuit 72-2 (or 72-1) or the storage area 72-12(or 72-11) is extracted, and now, the output of the memory circuit 72-2(or 72-1) or the storage area 72-12 (or 72-11) is inputted by way of theselection circuit 75a to the white level algorithm circuit 77. Then, theprocessing described above is performed subsequently by the white levelalgorithm circuit 77 so that the white level value may have anappropriate value to update the white level.

Consequently, even in such a case that paper sheets whose ground coloris white have been read till now and blue print paper sheets of adifferent ground color are to be read subsequently, the white levelinformation correction apparatus copes with this sufficiently and canperform analog to digital conversion with a high degree of accuracy.

Then, the image signal after digital conversion by the analog to digitalconversion circuit 60A or 60B is transferred to the image processingsection 68A or 68B for next image processing such as, for example,emphasis processing to emphasize the contrast between white and black or"dither processing; binary digitization processing" for a net pointimage such as a photograph image as described hereinabove.

Further, in each of the image data processing systems D1 and D2, digitalinformation obtained from the analog to digital conversion circuit 60Aor 60B is sent, after it is processed by emphasis processing and/orbinary digitization processing by the image processing section 68A or68B, to the outputting section 90 as seen from FIG. 2, and paper frontface data and paper rear face data are transferred from the outputtingsection 90 to the host computer (not shown).

Upon such transfer, data (paper front face data) from the firstoperating image reading unit 412 from between the first optical imagereading unit 412 and the second optical image reading unit 414 fromwhich paper image information is to be read out first are firsttransferred successively by way of a data transfer line. Meanwhile, data(paper rear face data) from the later operating image reading unit 414from between the first optical image reading unit 412 and the secondoptical image reading unit 414 from which paper image information is tobe read out later are temporarily stored into the DRAM 92, and, afterthe data from the first operating image reading unit 412 are transferredcompletely, the stored data from the later operating image reading unit414 are successively transferred at a rate higher than the transfer rateof the data from the first operating image reading unit 412 by way ofanother data transfer line.

Consequently, even if image reading by the later operating image:reading unit 414 is started before image reading by the first operatingimage reading unit 412 is completed, data within the overlapping periodcan be held with certainty. Besides, data from the later operating imagereading unit 414 from which data are to be transferred later can betransferred rapidly to the host computer side.

Accordingly, even where the image reading units 412 and 414 are disposedin the proximity of the paper transport path in order to achieveminimization, reduction in weight and compaction of the apparatus, dataof the front and rear faces of a paper sheet can be transferred to thehost computer side before the paper sheet is discharged to the stackingmechanism 500. Consequently, even if paper sheets are successivelytransferred at a high speed while achieving minimization, reduction inweight and compaction of the apparatus, data of the front and rear facesof each paper can be read and transferred to the host computer sidesatisfactorily.

In this instance, the paper leading end detection circuit 450 detectsthe leading end of a paper sheet based on a paper end detected for thefirst time, and then when the MPU circuit 150 receives such paperleading end detection signal as an interruption requesting (IRQ) signalfrom the paper leading end detection circuit 450, the MPU circuit 150develops, in response to the interruption requesting (IRQ) signal, acommand signal to read the front face of the paper sheet. As a result,also the selection circuit 96 is switched to the paper front face dataside.

Meanwhile, the paper trailing end detection circuit 451 detects thetrailing end of the paper sheet based on a paper end detected for thesecond time, and then when the MPU circuit 150 receives such papertrailing end detection signal as an interruption requesting (IRQ) signalfrom the paper trailing end detection circuit 451, the MPU circuit 150develops, in response to the interruption requesting (IRQ) signal, acommand signal to read the rear face of the paper sheet. As a result,also the selection circuit 96 is switched to the paper rear face dataside.

Where the paper leading end detection circuit 450 and the paper trailingend detection circuit 451 of such circuit construction as describedabove are employed, the leading end and the trailing end of a papersheet can be detected with certainty with a common circuit constructionand with a simple construction. Consequently, reading timings of paperfront face data and paper rear face data or reading switching timingsbetween them can be controlled precisely irrespective of the type of apaper sheet being transported. As a result, it is comparatively possiblefor the image reading apparatus to allow paper sheets of various sizesto be transported to read information on them.

The present invention is not limited to the specifically describedembodiment, and variations and modifications may be made withoutdeparting from the scope of the present invention.

What is claimed is:
 1. A white level information correction apparatusfor an image reading apparatus wherein image information of a papersheet being transported along a paper transport path is optically readat a fixed location of said paper transport path using an optical imagereading unit and analog data obtained by said optical image reading unitare converted into digital data using white level information of theimage information as a reference, comprising:a plurality of storagemeans for storing information of a plurality of white levels each to beused as to the reference; data magnification variation means formultiplying white level information from a first one of said storagemeans in which the white level information being currently used as thereference for the conversion of analog data originating from a currentlyused paper sheet into digital data is stored by a coefficient which isdetermined based upon a background color of another paper sheet which isto be read subsequently and may have a different background color fromthat of the currently used paper sheet; and data write control means forstoring white level information varied in magnification by said datamagnification variation means into a second one of said storage meansdifferent from the first storage means so that the white levelinformation in the second storage means may thereafter be used as thereference for the conversion of analog data.
 2. A white levelinformation correction apparatus for an image reading apparatus asclaimed in claim 1, wherein said pluarity of storage means areconstituted from memory circuits independent of each other and capableof storing a plurality of pieces of white level information to be usedas indices to the conversion reference.
 3. A white level informationcorrection apparatus for an image reading apparatus as claimed in claim1, wherein said plurality of storage means are constructed from a singlememory circuit having a plurality of storage areas capable of storing aplurality of pieces of white level information to be used as indices tothe conversion reference.
 4. A white level information correctionapparatus for an image reading apparatus as claimed in claim 1, whereinthe magnification rate of variation of said data magnification variationmeans is variable.
 5. A white level information correction apparatus foran image reading apparatus as claimed in claim 1, wherein said datawrite control means includes selection means for storing white levelinformation varied in magnification by said data magnification variationmeans into the second one of said storage means.
 6. A white levelinformation correction apparatus for an image reading apparatus asclaimed in claim 1, wherein said data write control means includes:firstselection means for selectively outputting white level informationvaried in magnitude by said data magnification variation means or whitelevel information from one of said storage means; a white levelalgorithm circuit correcting the white level information selected bysaid first selection means based on the data obtained by the opticalimage reading unit; and second selection means for storing an output ofsaid white level algorithm circuit into a selected one of said pluralityof storage means to update the stored data.
 7. A white level informationcorrection apparatus for an image readingapparatus as claimed in claim6, wherein said white level algorithm circuit includes: a digitalcomparison circuit for comparing digital data obtained by said opticalimage reading unit and the white level information being currently usedas the reference with each other; and a white level informationcorrection circuit for correcting the white level information selectedby said first selection means in response to a result of comparison bysaid digital comparison circuit.
 8. A white level information correctionapparatus for an image reading apparatus as claimed in claim 6, whereinsaid white level algorithm circuit includes:a control signal productioncircuit for comparing digital data obtained by said optical imagereading unit and the white level information being currently used as thereference with each other and outputting, in response to a result of thecomparison, a control signal indicating that the digital data has apredetermined value; a counting circuit for counting the number of timesby which a control signal is outputted successively in a direction of aline from said control signal production circuit; and a white levelinformation correction circuit for correcting the white levelinformation selected by said first selection means in response to acount value of said counting circuit.
 9. A white level informationcorrection apparatus for an image reading apparatus as recited in claim6, said white level algorithm circuit comprising:a control signalproduction circuit for comparing digital data obtained by said opticalimage reading unit with information of a plurality of white levels ofdifferent brightness levels each to be used as the reference andoutputting, in response to a result of the comparison, a control signalindicating that the digital data has a predetermined value; a countingcircuit for counting the number of times by which a control signal isoutputted successively in a direction of a line from said control signalproduction circuit; and a white level information correction circuit forcorrecting the white level information selected by said first selectionmeans in response to the control signal from said control signalproduction circuit and a count value of said counting circuit.
 10. Awhite level information correction apparatus for an image readingapparatus as recited in claim 6, further comprising switching controlmeans for switching said second selection means so that, when a papersheet to be read subsequently has the same background color as that ofanother paper sheet which has been read last, an output of said whitelevel algorithm circuit is stored into the first storage means, but whenthe paper sheet to be read subsequently has a different background colorfrom that of the paper sheet which has been read last, the output ofsaid white level algorithm circuit is stored into the second storagemeans.
 11. A white level information correction apparatus for an imagereading apparatus as recited in claim 6, wherein said white levelalgorithm circuit includesa digital comparison circuit for comparingdigital data obtained by said optical image reading unit withinformation of a plurality of white levels of different brightnesslevels, and a white level information correction circuit for correctingwhite level information selected by said first selection means inresponse to the brightness level of the digital data based on a resultof comparison by said digital comparison circuit.
 12. A white levelinformation correction apparatus for an image reading apparatus asrecited in claim 11, whereinsaid digital comparison circuit includes afirst comparison section for comparing digital data obtained by saidoptical image reading unit and a first white level reference valuehaving a high brightness level with each other in magnitude, a secondcomparison section for comparing the digital data and a second whitelevel reference range which is lower in brightness level than the firstwhite level reference value to detect whether the digital data is withinthe second white level reference range, and a third comparison sectionfor comparing the digital data and a third white level reference valuewhich is lower in brightness level than the second white level referencerange with each other in magnitude, and whereinsaid white levelinformation correction circuit is constructed such that, when said firstcomparison section detects that the digital data is higher than thefirst white level reference value, said white level informationcorrection circuit increases the digital white level informationselected by said first selection means, but when said second comparisonsection detects that the digital data is within the second white levelreference range, said white level information correction circuitdecreases the digital white level information selected by said firstselection means, but otherwise when said third comparison sectiondetects that the digital data is lower than the third white levelreference value, said white level information correction circuitinhibits correction of the digital white level information selected bysaid selection means.
 13. A white level information correction apparatusfor an image reading apparatus as claimed in claim 1, further comprisingswitching control means for determining based on data obtained from saidoptical image reading unit whether white level information should bevaried in magnitude by said data magnification variation means andautomatically controlling selective switching of said first selectionmeans.
 14. An image reading apparatus, comprising:a paper transport pathalong which a paper sheet from which an image is to be read istransported; an optical image reading unit for optically reading, at apredetermined location of said paper transport path, image informationfrom a paper sheet being transported along said paper transport path;analog to digital conversion means for converting analog data obtainedby said optical image reading unit into digital data using white levelinformation of the image information as an index to a conversionreference; and a white level information correction apparatus forcorrecting white level information to be used as an index to theconversion reference of said analog to digital conversion means; saidwhite level information correction apparatus including:a plurality ofstorage means for storing information on a plurality of white levelseach to be used as the reference; data magnification variation means formultiplying white level information from a first one of said storagemeans in which the white level information being currently used as thereference for the conversion of analog data originating from a currentlyused paper sheet into digital data is stored by a coefficient determinedbased upon a background color of another paper sheet which is to be readsubsequently and may have a different background color from that of thecurrently used paper sheet; and data write control means for storingwhite level information varied in magnification by said datamagnification variation means into a second one of said storage meansdifferent from the first storage means so that the white levelinformation in the second storage means may thereafter be used as thereference for the conversion of analog data.